I think it's for rabbits. There is a warren of them nearby and they like to come to our yard where the play area used to be and eat grass and clover and such. Sometimes they come right up to the house. Possibly, Firestar is waiting for them to get close to the door so he can play the big "boo" on them. As long as he doesn't smash his face in the process.
Since I was down there with the camera I took a couple of shots. Son had taken some a couple of days ago, too. Here they are.