I agonize... but it's tolerable.

Some dogs are more sensitive to certain letters of the alphabet.
I've done this with Puppies mostly.

Just run through the Alphabet, saying the letter, and an additional sound the letter is/can be associated with. Like...

A, Am, Ahh, All
B, Bee, Boo, Baa
P, Pee, Paa, Poo
and so on.

Look for a response. Ears perking, cocking it's head, anything which it reacts to. Speak them slowly, repeat them, and see how it reacts.
Give that a try. Then you may have a starting "letter" (s), then you can expand on that start.

Have a good Day !
S.W.