catching vomit - why do we do these things?

so the other day we went to roller derby, (which I was very excited about, a family outing weeeeeeeeeee...)
on the way there squeaky decided he would have a little vomit.

now before becoming a parent I can tell you unequivocally that I wound not have put my hands out to catch his vomit.

However, now I find that my first instinct is to put my hands up to his mouth and make sure I catch anything that comes out.
Why?!
Why would I do such a thing?
 Seriously, Why do we catch Vomit?
its disgusting, it smells, but for some reason catching it in your hand is so much more important, because is you don't catch that shit is going to go every where, you are going to have a toddler running around covered in vomit, their clothes, and jackets, and as if guilt by association your clothes will also become contaminated with vomit - better to be on you hands than on your clothes - or the car seats.
oh dear god the car seats - travelling with the smell of vomit in the car.
no no.
that's all good Ill just collect it all in my hand at least then its contained.

and even now after running though this in my head I still really don't understand why something that I find so disgusting is now just an automatic reaction.

Oh how my life has changed.