The exclamation point is a curious choice here. I’d be more inclined to go with a question mark. As in Hum? Hmm? Or even a period. I’m not sure how you’d exclaim Hum!
– unless you’re trying to get someone to hum a tune
– Unless you were an SS Officer trying to cover the sounds of your crimes with the humming of your victims . In that case, Hum! makes a lot of sense.
Not so much.