Why can't a nose be 12 inches long?

Behind the Groan

Twelve Inches Underfoot

A foot is both a body part and a unit equal to twelve inches. The setup makes a nose sound as though it is being measured, then the punchline switches from length to anatomy. Keep the question casual so the exact number feels like an ordinary detail. A brief pause before “a foot” gives listeners time to picture an unusually long nose before the second meaning lands.