Sneezing, what a useful and enjoyable function. In the English speaking world, we make the noise “Ahh-choo” when we sneeze, presumably because that’s what our parents did. This noise has a useful social purpose. We are conditioned from childhod to expect a (potentially loud) “CHOO” if anybody makes an “Ahh-” sound.
On the other hand…
Often Germs don’t say ‘ahh. Sneezing is accompanied by a loud ‘KAH’ sound from the back of the throat. It always makes me jump. It’s probably my paranoia, but I suspect many are secretly looking out of the corner of their eye to see if they made you jump;-)
Realistically, I am sure there is an valid social purpose for the this; maybe there is less snot mist from a KA than a CHOO? Maybe you don’t need a hanky?