Ketchup and Rubber Buns

DAD: Ok, so after every question i ask you you must say ketchup and rubber buns.
KID: Gotcha.
DAD: what did you buy at the store?
KID: Ketchup and rubber buns.

DAD: What did you have for dinner?
KID: Ketchup and rubber buns.
DAD: What do you do when an old lady crosses the street?
KID: Ketchup and rub....... HEY