42 minutes into the film, the dog runs off into the woods. You hear the dog yelping, but do not see what is happening to it. Later in the film, you see what appears to be the dog's body, but he sits up and reveals himself to be partially transformed into one of the creatures.
Early in the movie the husband is investigating something gross and the dog is sad about it. The gross thing is really bad in the dog's opinion and he is sad his master is touching it.