Rex, Attack!

This postman is working on a new beat. He comes to a garden gate marked BEWARE OF THE PARROT! He looks down the garden and, sure enough, there's a parrot sitting on its perch. He has a little chuckle to himself at the sign and the parrot there on its perch. He opens the gate and walks into the garden. He gets as far as the parrot's perch, when suddenly, it calls out: "REX, ATTACK!"