Expecto Atronum?

My five-(soon to be six-)year-old is running around waving a Burger King toy (the stick that makes the Patrick Star top spin) yelling, "Expecto Atronum!" at his brother. Thanks, Jo Rowling, for a creative way for my kids to fight. Hmmm. Apparently, the three-year-old thinks that spell turns him into a cat. Maybe when it's miscast (it should be "Expecto Patronum"), it does turns its subject into a cat. Meeow.