My 5 month old baby boy seems to get chills down his spine at random times - what could this be? (I'm worried)?

My son has always done the same (he's almost 11 months) and I've noticed my friends baby does the same too. I don't think it's anything to worry about, they probably do it for the same reasons adults do, it's sometimes easy to forget that they are miniature humans and will have a lot of the same unexplainable bodily functions as us! I'm sure it's just when they get a sudden chill for some reason, or perhaps even when thinking about something they dislike like adults. Sure there's no harm ringing the doc to put your mind at rest, but I certainly wouldn't be jumping to any fears such as Tourette's!