In the Ice Age: Continental Drift movie, when Scrat dives into the sea with help of a large stone to get the acorn, his bones start disappearing as he goes down. Why does that happen?
This is a bit of artistic license on the part of Blue Sky's animators who did this to exaggerate the effects of water pressure on him.
In the short, Scrat is dragged under fairly rapidly by the rock, and so the water pressure exerted on him would build up extremely quickly and with great force. However, this being a cartoon, Scrat merely continues his effort to retrieve the acorn/map with his body crushed and floppy. It's animation physics :)