Non bene flat flammam qui continent ore farinam.
(Medieval)

He does not blow a flame out well who has flour in his mouth.

(pron = nohn BEH-neh flaht FLAHM-mahm kwee KOHN-ti-neht OH-reh fah-REE-nahm)

Comment: My first thought after reading this proverb was of an old “Little
Rascals” episode in which the children were competing in a whistling contest.
One of the more devilish of the Rascals offered the best whistler some saltine
crackers just before the competition. Of course, with a mouth dried up by the
cracker, his whistling ability disappeared. Crackers, of course, made of
flour, would be an example of a mouth full of flour.

This is one of those down to earth, practical proverbs: don’t try to do
something for which you are not prepared or if something impedes your ability
to do it. Blowing out a candle is no big deal—unless the candle is about to
cause a fire—and unless you’ve just eaten a handful of crackers!