Well... they wobble their heads lol. Some more than others. Sometimes they corkscrew its so bad. My girl really doesn't have much of a wobble. Mostly when she's really excited, like when feeding her head bobs up and down as she gets ready to strike.
Thanks Connie,
I noticed my bumble bee doing this the other day and it kind-of freaked me out. Glad to hear that its common in spiders.