If a Slurtle has a mineral in it's inventory and it loses aggro on a player it will stop moving entirely. It will respond if the player attacks it again but if the aggro is lost the same thing will happen.
Also instead of dropping the entire stack when it gets hit it only drops a single mineral. The rest of the stack still drops if the player kills the slurtle. I don't know if that one is a bug but I thought i'd mention it.
In ANR beta
Drop a stack of stones. Allow slurtle to eat it (The chewing animation). Hit the slurtle before it finishes eating. Run off screen to lose its aggro. Voila, you've traumatized a slurtle to the point of it being unable to move.