Notes

The key can be used on the door, located deeper in the dungeon.
Whilst no experience is gained when fighting these monsters, there are also level 25 Experiments, which offer a very good rate of experience per hour.

Tactics

These monsters don't give experience when fought, so there is no reason to kill them but for the quest. You cannot kill them once you obtain the Key. If attempted, you will receive the message: "You don't have the heart to kill the poor creature again."

Examine

It has a key hanging from its collar.

Drops

Bones (100%), Key