^ well have a look at this video.
http://www.youtube.com/watch?v=qAp5Y4YbYP0 Tells you almost everything you may want to know about reverse swing, described by the great Wasim himself. And he mentioned that when Saqlain Mushtaq first came into the team, he spat on the ball. And him and waqar warned Saqlain to never do that, otherwise Ws will kill him