Il ne marche qu’à coups de fouet = He works only when he is compelled.
Fouetter
Fouette, cocher! = Fire away! Go ahead!
Four
Il fait noir comme dans un four = It is as dark as pitch.
[Molière, Le Sicilien, ii.]
Faire un four = To make a blunder.
Cette pièce a fait four = That piece was a failure, a frost.
On ne peut être au four et au moulin = One cannot be in two places at the same time.