Why do dogs eat their own vomit?

Question

My friend had a dog named Friend Freak. After throwing out a host of food, he ate it all up again. Why?

Answer 1

Uhmm, probably the same reason why they eat their f***s. But whatever, it's normal since most dogs like all that nasty stuff like smelly shoes, and  swampy ponds so vomit might turn out to be the most attraction thing to them.

Also, another reason could be that he was hungry and the vomit still had some distinguishable pieces of tasty foods in there, so why not?