how small of a hole can a mouse fit through

A mouse can typically fit through holes roughly as small as 16 millimeters (about 5/8 inch) in diameter. Smaller mice, such as younger or starving ones, may squeeze through slightly smaller holes, but 16 mm is generally the critical size found in experiments. Mice have highly flexible rib cages and collapsible skeletons, which allow them to flatten their bodies and pass through tight spaces around the size of a pencil diameter or slightly smaller. Holes smaller than about 14-15 mm generally prevent mice from squeezing through, though slight variations can occur depending on the mouse's size and condition.