Axolotl reposition themselves when the game pauses, instead of freezing immediately. This happens with Axolotl on land as well as in water. As far as I can tell, they are the only mob to do this.

Steps to Reproduce:
1. Open a singleplayer world which allows pausing
2. Spawn an Axolotl
3. While looking at the axolotl, pause the game with F3+ESC