Son acting like animals

So my 2 year old son keeps acting like a dog and a cat or a cow. Mainly a dog. When someone comes up to him or me he barks at them. When we go to the store he gets in the buggy on all fours and stays barking at people. I tell him it is not nice and I think he has stopped, not 100% positive. Now almost all day he has been barking non stop and I don't know what to do. I don't mind it but I don't want him to do it all the time thinking it's ok.