You have to watch for things like muscles tensing. There are a lot of noises and expressions people make too, but those are different per person of course! But you can tell if someone gets harder or twitches a lot in your mouth, and...
Playing with their balls helps. Because you can notice that they draw up closer when they're ready to finish, too. I think pretty much everyone does that.
Re: video
Playing with their balls helps. Because you can notice that they draw up closer when they're ready to finish, too. I think pretty much everyone does that.