Rumpology

Rumpology is the purported ability to glean psychic or other information from a subject using ESP or clairvoyance specific to arses. If this sounds like PIDOOMA, you may be on the right track, but this must be pulled out of someone else's rump.

Not to be confused with a posteriori reasoning, which may or may not be bullshit, rumpology is like phrenology, but using the tail end.

Depending on the temperature of the subject, this might be either cold reading or hot reading.

Possibly the most famous rumpologist is American astrologer Stallone — yes, mother of the  She put the ass in astrology.

Buttocks reflexology
John C. McLachlan, a professor of medical education, submitted a hoax abstract for a presentation to the The Jerusalem Conference on Integrative Medicine in 2010 on the topic of buttocks reflexology. The abstract claimed that a homunculus on the buttocks corresponded to that could be used for reflexology. The purpose of the accepted submission was to demonstrate the degree of credulousness of alternative medicine, specifically integrative medicine. The diagram that was presented with the abstract showed buttocks with the brain's of body parts superimposed upon each cheek.