I want to see what happens when you keep it in really strong box longer then its necessary because those faces were just getting better and better and if there would be spikes from inside would it get hurt or it would adapt to them?
If the spikes were blunted, it'd probably adapt Otherwise, the spikes would puncture the skin. The yukkuri wouldn't die, though. Where would the filling go?
...come to think of it, it'd probably adapt... So, if you somehow managed to form spikes on its body...