The Exploding Hedgehog Room

This is an encounter that I have sprung on multiple groups through the years to good effect. It is a puzzle with difficulty that varies based on how much the party cares for the wellbeing of an innocent hedgehog, and it tends to go over pretty well with most groups.

The Setup
The party finds themselves locked in a room resembling a science lab of an appropriate style to match the rest of the area the encounter is embedded in. The lab consists of a main lab with a table, a testing chamber, and a hedgehog pen. To leave the lab, the party must locate a key that is hidden somewhere in the science lab to be able to unlock the door and leave.

The Rooms
The main lab is clean and the table holds several pieces of scientific equipment and a journal. The journal belongs to a wizard who claims to have been studying exploding hedgehogs. The last journal of the entry explains that the wizard has gained all the knowledge that they can, that they have left enough food and water to last the hedgehogs the rest of their lifespans, and that the wizard will teleport out of the lab, leaving it locked from the inside, because one of the hedgehogs ate the key and will probably never pass it from its stomach.

The testing chamber is made of a material that is strong enough to be relatively unaffected by small explosions. There are a number of scorch marks on the floor of the testing chamber. The door to the testing chamber is heavy, but has slot that can be opened without opening the rest of the door that is large enough to shoot an arrow or cast a spell through.

The hedgehog pen uses magic to maintain an ideal habitat for the hedgehogs. There are 6 hedgehogs, each with one of the numbers 1 through 6 on its belly, which do, in fact, explode upon their deaths. When I run this encounter in 5th edition Dungeons and Dragons, the hedgehogs have these stats with the additional trait that upon hitting zero hit points, they explode, dealing 4d8 fire damage to anyone within a 5ft radius of a hedgehog when it explodes. The key is inside hedgehog number 6. The hedgehogs are generally friendly and appear to be used to being handled and tested on.

Notes
In practice, this encounter usually ends with the party locating the key inside hedgehog number six, but accidentally killing the poor creature in their attempt to extract the key without harming the hedgehog. It is worth noting that there is no downside to simply detonating the hedgehogs one by one until a key is found, but there should definitely be ways to get the key out non-lethally. I prefer to have this require a roll based on the method of getting the key out. If the party tries to induce vomiting, they need to have someone roll to make sure they only induce vomiting and don't poison the hedgehog to death, for example. This encounter works best when you let the party come up with their own solution with the items and abilities they have on hand, rather than trying to think of a single solution that the party has to figure out, so I try to be open-minded in what may or may not work as a solution to get the key.