A few things come to mind... first is that Calvin really doesn't actually spend time with anyone, but Hobbes and his mom. Sure he goes to school and occasionally is seen interacting with Moe and Susie in the wild... but he spends most of his time alone with Hobbes. Actually, all the long term interaction between the two is done in either water balloon or snowball fights . The only one who spends near as much time with Hobbes is Calvin's mom... and if you watch her, every once in a while she'll stop dead and just look at Hobbes. Many of those times she looks kind of spooked. I think the most egregious moments is during one of my pivotal moments in the series. The Robbery arc.
This arc is all about Calvin and family on vacation and Calvin leaves Hobbes behind... Calvin just about has a nervous break down so they cut the vacation short and drive home. Once there they discover they've been almost robbed. Almost. The scene has stuff gathered and it looks like the robbers freaked and ran. Like dumped their inventory and bolted ran. In the end nothing actually left the house and Hobbes claimed to have run them off or alluded to having eaten them (claiming they were horrible tasting, though that may have been from elsewhere)... Its been a while since I've read it. Hobbes is in the room on the TV or a high shelf (either way Calvin couldn't have gotten him up there) in the same room. Again this part may be time distorting memory, but I remember Hobbes was last seen in Calvin's room. I do remember checking that. Always thought that it would make a good one shot to have the cops humor Calvin and ask for a description of the guys, the description matches a pair of career criminals... only to either find them terrified and scared straight or just plain disappear. I can't remember any follow up on this, which always bugged me.
The main theory is that Calvin's active imagination is animating Hobbes in his head... only the only time I can remember Hobbes actually being present during those hallucinations are if Calvin in narrating and trying to avoid eating something gross or if the transmogrifier is involved. There is one arc about Calvin getting turned into something and getting stuck... and panicking. His mom basically blew it off (he looked physically normal to her)... but he was really concerned. I also remember a Star-Bellied Sneetches moment with the gun where Calvin and Hobbes shot each other until the have no clue who was who.
So at least some of the time Calvin is stuck in in a hallucination or illusion of some type. Which would explain what was happening here... only there is that Robbery Arc. This kind of power could explain why the robbers freaked out... only that means Calvin isn't doing it. He was at least dozens of miles away, so it has to be Hobbes doing it. Then we get to iconic feature of the series, one mentioned in the tread title. Calvin barely gets the door open... and is flying tackled before he can get in the house at all. Try working out the physics of that. He doesn't just fall over either... he ends up a dozen feet or so away. Across a paved/stone path.... by doing multiple somersaults using the tiger as part of the movement. Hobbes doesn't end up torn up and Calvin is dirty, not road rashed.... so how does he manage to do that? Stuffed animals just aren't stiff or reactive enough to compensate for that.
This brings up one of the constant things that bugs Calvin's mom about Hobbes... he keeps ending up in different rooms. Not just the Robbery arc, but on day to day. she leave Hobbes in Calvin's room or in the laundry room and Hobbes is still there at the front door... on the opposite side of the house. So Hobbes is apparently self mobile in situations that can't be written off as Calvin hallucinating. Which means Hobbes can actually manipulate objects besides himself. He has helped Calvin move stuff before.
One more thing on this section... Hobbes is repeatedly referenced to eat. Tuna, random stuff. Calvin is always getting him food, which is eaten. Which is traditionally the way to appease helpful spirits and such. Even Hobbes scarf can be viewed as a gift to him. Lets see watches the kids, guards house, eats stuff. Hobbes and Calvin are both aware of his body being that of a stuffed animal. Its washed in the machine and repaired with sowing. This section is largely to establish what Hobbes can actually do as an entity.
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That out of the way, lets move onto Susie. First, the major changes when she can see Hobbes as Calvin does is that she can see/feel what Calvin is rambling about when she has teased him doing this in the past. This should actually be covered.... whether as her making the connection out loud or doing it as an aside in her head is writers choice. The first is going to lead to have Calvin doing a "Why did you think I kept reacting like that?' moment and the latter is good for setting herself up teasing him later and then explaining things later on.
The second is how old are they? This is important for many reasons. Too old and Calvin is going to get lots of flack for the stuffed tiger. I'd suggest this being the year after the comics. leaving them around 8 and in second grade. The older they are the more likely they can justify fire. Which will both please Hobbes and leave a smoke trail so they can be found in the morning.
This arc is all about Calvin and family on vacation and Calvin leaves Hobbes behind... Calvin just about has a nervous break down so they cut the vacation short and drive home. Once there they discover they've been almost robbed. Almost. The scene has stuff gathered and it looks like the robbers freaked and ran. Like dumped their inventory and bolted ran. In the end nothing actually left the house and Hobbes claimed to have run them off or alluded to having eaten them (claiming they were horrible tasting, though that may have been from elsewhere)... Its been a while since I've read it. Hobbes is in the room on the TV or a high shelf (either way Calvin couldn't have gotten him up there) in the same room. Again this part may be time distorting memory, but I remember Hobbes was last seen in Calvin's room. I do remember checking that. Always thought that it would make a good one shot to have the cops humor Calvin and ask for a description of the guys, the description matches a pair of career criminals... only to either find them terrified and scared straight or just plain disappear. I can't remember any follow up on this, which always bugged me.
The main theory is that Calvin's active imagination is animating Hobbes in his head... only the only time I can remember Hobbes actually being present during those hallucinations are if Calvin in narrating and trying to avoid eating something gross or if the transmogrifier is involved. There is one arc about Calvin getting turned into something and getting stuck... and panicking. His mom basically blew it off (he looked physically normal to her)... but he was really concerned. I also remember a Star-Bellied Sneetches moment with the gun where Calvin and Hobbes shot each other until the have no clue who was who.
So at least some of the time Calvin is stuck in in a hallucination or illusion of some type. Which would explain what was happening here... only there is that Robbery Arc. This kind of power could explain why the robbers freaked out... only that means Calvin isn't doing it. He was at least dozens of miles away, so it has to be Hobbes doing it. Then we get to iconic feature of the series, one mentioned in the tread title. Calvin barely gets the door open... and is flying tackled before he can get in the house at all. Try working out the physics of that. He doesn't just fall over either... he ends up a dozen feet or so away. Across a paved/stone path.... by doing multiple somersaults using the tiger as part of the movement. Hobbes doesn't end up torn up and Calvin is dirty, not road rashed.... so how does he manage to do that? Stuffed animals just aren't stiff or reactive enough to compensate for that.
This brings up one of the constant things that bugs Calvin's mom about Hobbes... he keeps ending up in different rooms. Not just the Robbery arc, but on day to day. she leave Hobbes in Calvin's room or in the laundry room and Hobbes is still there at the front door... on the opposite side of the house. So Hobbes is apparently self mobile in situations that can't be written off as Calvin hallucinating. Which means Hobbes can actually manipulate objects besides himself. He has helped Calvin move stuff before.
One more thing on this section... Hobbes is repeatedly referenced to eat. Tuna, random stuff. Calvin is always getting him food, which is eaten. Which is traditionally the way to appease helpful spirits and such. Even Hobbes scarf can be viewed as a gift to him. Lets see watches the kids, guards house, eats stuff. Hobbes and Calvin are both aware of his body being that of a stuffed animal. Its washed in the machine and repaired with sowing. This section is largely to establish what Hobbes can actually do as an entity.
---
That out of the way, lets move onto Susie. First, the major changes when she can see Hobbes as Calvin does is that she can see/feel what Calvin is rambling about when she has teased him doing this in the past. This should actually be covered.... whether as her making the connection out loud or doing it as an aside in her head is writers choice. The first is going to lead to have Calvin doing a "Why did you think I kept reacting like that?' moment and the latter is good for setting herself up teasing him later and then explaining things later on.
The second is how old are they? This is important for many reasons. Too old and Calvin is going to get lots of flack for the stuffed tiger. I'd suggest this being the year after the comics. leaving them around 8 and in second grade. The older they are the more likely they can justify fire. Which will both please Hobbes and leave a smoke trail so they can be found in the morning.