Adam is right on.(As usual)

I myself have 2 spiders(male and female) and one does it more than the other(barely noticeable). They are great snakes and would not trade them for the world. My one bobble heads mostly at feeding time, when excited.

Spiders are one of the best morphs you can have in your collection, they eat great, act great, grow nicely and breed well. I would not hesitate to recommend spiders to anyone collecting BP's. Their combos are the amazing!

It's not like seizures or ANYTHING like that. People just can't help but want to put the 2 VERY DIFFERENT behaviors in the same category and say defect!