I'm stumped. Rat seems to disappear behind the shoe rack.

A couple of times now, I've seen it run quickly under the shoe rack to never be found again. We've been keeping the doors closed for the past few days, I've emptied the room. It's literally just walls, and an empty shoe rack. No holes. nowhere for it to go. It's not on the underside, behind, corners. I've moved it around a bunch of times...nothing. WHERE THE HELL is it going?