No, seriously. I assumed they were jumping from the chair seats piled high with books etc-- though there's the question, how did they get up the chair legs to the seats in the first place? But I've pushed all the chairs back. Mice would have to do a death-defying leap, diagonally upwards across about fourteen inches. So what? Do they swarm up the lamp cord? Wriggle up the table legs and use heel grips for the overhang of the table top? Parachute?
Because every morning there's a tiny turd waiting for me on the table, outside the tip-trap full of tasty flaxseeds the mouse is too dumb to go into. Rot it.