More Helen Blepper
Have deaf cat, can answer.
You kinda work it out slowly over time. When you have them from a kitten, it starts with you wondering when they're going to start reacting to their name or you calling them or coming home. Eventually a loud noise will happen right next to them and they won't even flinch. That's about when the thought that they might be deaf starts to form.
From there, you kinda test them out, making increasingly loud and sharp noises just behind them (so they can't see and react to that). Things that they've done in the past start to make more sense in the context that they may not be able to hear.
Eventually it gets to the point where you get confident enough to make a really unpleasant sound near them that would scare any other cat shitless like blowing a whistle or turning the vacuum or something like that and then you know for sure.
I'm sure there are tests that vets can do to confirm it but once you know, it's kinda obvious.
She was really sick and close to not getting better when we found her and when we took her to the vet we were told she had infections including in her ears. Vet said she might be deaf and then like the other reply to this said, you kind of just test it and can tell.
If you pet her from behind it clearly shocks her because she won't hear you coming and you can scream while she's asleep and she won't flinch. She also loves the vacuum.
She's Helen after Helen Keller (husband's idea) which I promise is more of an homage than a sick joke.
How can you tell your cats deaf and not... well.... just being a cat?
Yeah, parents thought one of our cats was deaf. But then we realized he can hear food from across the house, and was just being lazy / ignoring us.
Is this the face that launched a thousand bleps?
That is a beautiful blep.
Well it makes sense since Helen Keller is best known for having her tongue sticking out slightly.
ok, I'll just see myself out
Helen of Blep.
She also loves the vacuum.
Yup. She's deaf.
Linked another in the comments, here's a third of her in all her glory