Alex, the head is different on the leopard spider pieds than just a regular spider's head. That's really the only way to tell, and unfortunately, it's hard to describe. Greg Graziani had one available on his website earlier this year, and it was clearly different (the picture is no longer there otherwise I would tell you to check that out). As far as with pastels and spiders, the leopard trait does warp the body pattern a bit too. You won't confuse it with a normal on a pastel, but it's a bit harder to tell on a spider. That head is usually what you can know it by on the spider though. My suggestion would be to try to make it to a show Greg is attending later on this year when he has more available and to study them a bit, as he had the most of anyone else I saw last year, and I'm sure he'll have even more this year.