Lost his car keys in there, tell him you just don't know how it happened. Then make him move the machine so you can look behind, nope, no keys. Put that machine over there. Maybe they fell behind that bookcase...You get the idea.
My sewing area is in the basement and I have to deal with cobwebs in the rafters and behind things. I am so creeped out by these and hate to clean them up. When I want my son to use the shop vac on them, I hide dollar bills around the room and when he sweeps he gets what he finds.