"So when you shave what are you doing?" Mr F asks accusatorially
"What do you mean?... I'm switching the blades... that is your blade on the windowsill." Mrs F responds
Then thinking she gets where he's going with this she adds "You are shaving your beard, I am shaving what few hairs remain in my armpits... I do not think I am the one who is dulling the blade."
Mr F smiles sheepishly and replies simply "Oh... I guess not."