"If there is a 'glory hole' (a small hole, approximately three inches in diameter, which has been carefully carved), it may be used as a means of signaling from the stall. This has been observed occurring in three manners: by the appearance of an eye on the stool-side of the partition (a very strong indication that the seated man is watching you), by wiggling fingers through the hole, or by the projection of a tongue through the glory hole." -- Laud Humphreys