With so many great meat sandwiches on offer, it's easy to forget Arby's also sells Greek gyros. But what's in the chain's mysteriously named gyro sauce?

April is “Free Sandwich Month” at Arby’s. On Tuesday, the fast food spot announced that customers can score one free sandwich, wrap or gyro every week through the end of the month.

An Arby's order in a paper bag next to an Arby's drink carton and a portion of curly fries - Summer_Wind/Shutterstock ...