Howdo Mick,
Yes it could be yoghurt but if you consider the amounts of physical contact that's made with the stones on a daily basis from a large volume of visitors..it doesn't really add up. Just my opinion.

Messrs Beckensall and the Browns are still convinced that it's the real deal.
It's not as if spirals are unknown on Cumbrian monuments and Stan's rubbing of the carving cannot be dismissed out of hand.
I'm not sure this one will ever be done and dusted.

cheers
fitz