I'd say the other posters are just right. I did this as a child -- I hid my animal-shaped vitamins instead of taking them, because I didn't want to eat them. :-)
I tend to think it's empathy. My dc was at a group the other day when someone brought in a kitten. The other kids were all over it, very excited, and dc held back. The teacher commented, "NAME wasn't very interested in the kitten." I asked dc, and it turns out dc held back out of empathy -- dc felt the the poor kitten probably was overwhelmed and, as much as dc wanted to pet it, dc didn't want to add to its stress!
