I took Calvin and Jessica to the vet last Sat. When we go out, I usually put them in the same carrier. It's big enough, and they can console each other that they're going somewhere. When we get home, I open the door and they go sprinting out and run into their "house."
Well, I've left the carrier door off and the carrier on the floor since last week's trip. Every night, both of them will hop into the carrier and stay inside of it for a while, presumably to eat the hay in the litter box inside of it. At least that's what I, as a rational human, think they're doing.
From their point of view, maybe they're playing "Let's pretend."
Jessica: I'm gonna pretend we're on our way to a carrot farm.
Calvin: I'm gonna pretend we're going to a raisin factory.
Jessica: That sounds good. I'll go with you.
Eventually, they hop back out of the carrier and into the living room as a whole. If they do go on a pretend trip, they never bring me back any pretend souveniers, so they have to have visited a destination that revolves around bunny treats. :-)