Psychosomatic itching. Why does this happen?

Can anyone explain what is happening when thinking about certain things makes you itchy?

Since my scalp was itching terribly while reading the “electronic lice comb” thread, and someone else remarked that they were too, I’m wondering…

Why is this such a common experience?

Does this happen to other animals?

I can see how it might be a useful trait if being reminded of parasites creates a compulsion to groom.

I fully expect this thread to drop like a rock, but it would be nice if someone happened to write their masters’ thesis on this annoying phenomenon. I gotta know.

If anyone needs me, I’ll be in the shower.

I’ve scratched my head, but can’t come up with an answer.