What could be the cause of my dog's vomiting?

For a couple of months now my 1.5 y.o. Chi-Terrier does a motion like she will vomit. Sometimes it sounds like a dry cough... At times she vomits at times she does not. What might it be?

My daughter's dog does this when he is tearing into a rawhide 'bone'. When he gets a piece that is a size that he thinks he can swallow, he tries. But often it is too big or turned in a wrong direction, so he coughs it up to try again.
I don't know, but could this be what is happening?

he will do that if he ate grass

Have you had him checked for Kennel Cough? They gag, hack, sometimes vomit...have you had him around any strange dogs, or to a park where he might pick it up? It's highly contagious.

phrannie

my boyfriends dog did this because he had eatten something off the floor and his stomach was not digesting it so it would cause him to try and cough it up but nothing ever came out. eventually he had surgery and they found atlot of things in his stomach that were not spose to be there!