Not Twins

A very unattractive, mean acting woman walks into Wal-Mart with her two kids.
After shoving her way past several customers waiting to get carts, she says to the Wal-Mart greeter,
"Go through those carts and find me one that doesn't need oiling for once!"
"Yes Ma'am, happy to oblige," says the Greeter, and picks out a cart for her.
"Here you are, Ma'am, hope this one is okay," he says.
"If you'd get out of my way, maybe I could find out!" snaps the woman.
"Sorry, Ma'am," the Greeter says, standing aside and smiling, "And you and the twins have a nice day."
The woman snarls, "They're not twins, you moron! They don't even look alike."
The greeter smiles, "That's true, they don't, Ma'am. I just find it hard to believe you got laid twice."