I was just cleaning Mr. Bun-Bun’s cage and he was supervising as always. At one point I noticed him chewing something very thoroughly but I assumed it was hay since I had just put a fresh pile in his litter box. Then when I’m closing up the hay bag I notice the rubber band I use to close it is gone! My living room is clean and it couldn’t be anywhere else. 
I searched old topics and saw that people advised to feed more hay and pellets and fibrous foods to help push it through. He’s been chowing down on hay and pellets like a pig so I guess that’s a good sign? He usually gets a tablespoon or less of pellets but I just gave him a whole bunch. It was a small rubber band as well, one of the very thin ones of 1″ diameter. I just feel like such a bad mother!! I have no kids yet so I’m not used to thinking of things like rubber bands as potential hazards.
Thanks to this website and the info here I’m not panicking. I do have to leave for a few hours but once I get back I’ll check to see what the poo situation is like. As of now he appears totally normal.