Just as a head's up:
I received several comments & emails (all polite, which I appreciate) setting me straight on the topic of today's post -- apparently there is something to the seizure- and migraine-inducing capacity of the Ravelry website. So I (and Dr. Bartholomew of Psychology Today) were just plain wrong.
If you want more information, here's a website that gives more accurate information.
I've taken the post down. My apologies for spreading misinformation, which is exactly the opposite of what I set out to do here at Skeptophilia. But thanks for the readers who took the time to tell me to look deeper and reconsider what I'd written.