Ben did exactly the same thing! He had a screaming episode just before he started consistently saying mom, dad, dog, and hi/hey. (He's an early talker because his motor skills were delayed a bit.) Since he's started crawling, he only says dad now

and he barks at the dogs!

Seriously... it's definitely directed at them and meant to be a bark, but it sounds more like a scream.

We tell him no and tap him on the mouth so he'll associate the no with the appropriate body part, but that's about it.
That's what we do to everything at this point. We consistently say no (not "stop" or "don't" ... it's always "no") and we tap the body part that's doing whatever we're referring to so he'll understand why we're telling him no. *Soooooometimes* we can even say no from across the room and get the appropriate response. We *usually* get a giggle and he'll go back to doing whatever it was. Little booger! He KNOWS what he's doing!