Why do gas stations credit card machines make you pull your credit card out really fast?

Question

Why do gas stations credit card machines make you pull your credit card out really fast?

Answer 1

so nobody can shoulder surf you? and get your card number perhaps? (some ATM do the same thing)

Answer 2

Because if you pull it slowly, you might actually stop or slightly back up, giving a bad reading on the magnetic stripe.  That's why cashiers swipe them quickly as well, although sometimes, they're ridiculous.  

Just make sure you pull smoothly and straight out, so the reader can get a good read on the stripe.  I pull mine out about as fast as I put it in.