likely a roach nest as hotdog said, hopefully mrdrnose removes their collision hitbox in a future update to solve the issue of them creating collisions, I don't think they need an actual collision box unless you somehow have one up wear you can only throw stuff at it, but then that just gives you reason to explore weird game mechanics too instead of just beaming rocks at it.
You may be able to see the nest without moving the fridge, in which case you can hit it with a hammer/rock/crowbar/whatever you can swing while holding