I know someone who couldn't distinguish awl from all.

The first time I went into a Home Despot, I went in search of an awl. The clerks had no clue whatsoever. I went to a locally-owned hardware store. The owner said "sure" and asked "what kind do you want" pulling out a board from under the counter with about 6 or so awls attached to it.

Many laymen cannot hear the differences between the t in top, stop, pot, and city. They're all distinct, but the differences are not phonemically significant in US English.

Ceci n'est pas un seing.