1st 2 mistakes, good try/effort. 3rd mistakes onwards, fffffuuuuu... Lol
Given that over the course of a game, most people will make at least 3 mistakes.... which means you're going to say "fffffuuuuu" anyway... so why not save having to wait for the third mistake and just say "fffffuuuuu" from the start? LOL
Playing doubles we must inevitably lose many points, what kind of things can you usefully say to your partner when you lose a point?
Usually my harsh glare mitigates the need for words. Though on occasion I'll offer some tactical advice such as, "You know, the object of the game isn't to try to hit their racquets with the shuttle.". I'll also try to diagnose any issues my partner might be having with their game. For example, "With all the shots you've been hitting into the net I can only assume you think we are playing hockey.".