You were just walking around, as you found the hatch to under the playhouse, so as a curious child, you go into it. You can hear the squeals and laughter of the children just above you. Quiet humming comes from down the hallway, and you peek your head around the corner to check.

It's CatNap, one of the Bigger Bodies experiments. He is the only one left in his cell, as the other Smiling Critters were attending to the children up top.