Maddy has started to recognize that animals are different than people.
It's possible that she is also clever enough to realize that they have a different language and it's a language she has picked up and is now using to communicate with us. She has started to say "woof woof" whenever she sees an animal.
Yesterday she saw pictures of a cat and she pointed to it and said "woof". In Canadian Tire, she saw pictures of dogs on at least 5 different boxes (I'm now aware of the fact that almost every vacuum cleaner uses a picture of a dog on it's packaging) and started "woofing" at them.
Michael is encouraging this behaviour by saying "woof" back to her.
I'm thinking it might be best to try to teach her some English words instead.