For the question of volume, it depends on the stuffed animal because I've seen really small ans really big stuffed animals before.
If a class is full of water and you add an ice cube the water will spill, this happens because the volume of the water is equal to the volume of the glass. Ice cubes have volume too (of course) so if you add the volumes for the water and ice cube it would be greater than the amount of volume the flass can contain (which leads to the water spilling out of it).