This stone head from the Celtic era was found at Hendy farm, near Llanfairpwll, Anglesey. Heads like this were fairly common during the Celtic era; they are believed to represent gods and were used in ceremonies. Two common features to these relics are the flat head, probably to hold an offering, and the hole in the mouth, either to give the god a drink or to hold a pipe or a branch.

Source: http://www.anglesey-history.co.uk/anghist.html