I like to buy a variety of salad items for Calvin and Jessica, and one favorite of theirs is radicchio. Radicchio sort of looks like red cabbage except that it's red and not purplish. I will peel leaves off of the head to give them to eat until the head is smaller than my fist, at which time I'll give them the rest of the head, whole.
Well, it should come as no surprise that Jessica usually grabs the head and runs downstairs with it, leaving Calvin on the second floor of the cage wondering where the tasty radicchio went. If I remember, I peel off a chunk before I put the head into their cage, so when Jessica grabs it and runs off, I have some to hand to Calvin (much like how Jessica now steals her own carrot while still thinking she's stealing Calvin's - see #1 under Tails of Sibling Rivalry in the Sept. 05 archive.)
The buns are good at sharing the litterbox, water bowl, etc., but when it comes to food, there is no such thing as yours and mine or his and hers. It's all Jessica's :-)