Is this the face of the devil? Art historian Chiara Frugoni spotted a face that Italian renaissance master Giotto snuck into a fresco in the Basilica of St. Francis in Assisi:

The face, with hooked nose and an evil smirk, is hard to see from the ground. [...] The basilica's chief restorer, Sergio Fusetti, said the devil image may have been a joke by Giotto aimed at somebody he had quarrelled with.

I can't wait for the new Dan Brown novel about this! ;) Link