“A Multidisciplinary Approach to Ritual Enema Scenes on Ancient Maya Pottery”, Peter A. G. M. de Smet, Nicholas M. Hellmuth1986-06 (, )⁠:

There are various enema scenes on classic Maya pottery, which undoubtedly represent rituals and may well indicate that the ancient Maya took intoxicating enemas in a ritual context. This idea is quite contrary to the traditional view that the ancient Maya were a contemplative people, who did not indulge in ritual ecstasy.

The occasional display of vomiting actors would seem to provide a plausible reason why the Maya opted for rectal application.