He can't what?
Missed the pun.
Apparently.
darn 1 (därn)
v. darned, darn·ing, darns
v.tr. To mend (a garment, for example) by weaving thread or yarn across a gap or hole.
v. intr. To repair a hole, as in a garment, by weaving thread or yarn across it.
n. A hole repaired by weaving thread or yarn across it: a sock full of darns.
[French dialectal darner, perhaps from Norman French darne, piece, from Breton darn.]