Regarding one or more persons inserting into another's anorectum, rapid thrusting with considerable girth especially for a prolonged duration must constitute criminal negligence at the least, worldwide without limitation.
"Midway up the [surgical] anal canal lies the dentate line (pectinate line). This marks the true mucocutaneous junction between somatically innervated squamous epithelium distally and the viscerally innervated columnar epithelium proximally."
"Perianal Abscess/Fistula Disease." Clinics in Colon and Rectal Surgery. 2007 May; 20(2): 102-109. PMC2780182.
"Internal hemorrhoids are lined by columnar epithelium. Near the dentate line, there may be transitional epithelium. This mucosa is viscerally innervated, which means patients will report sensations such as vague fullness and pressure, but do not perceive touch, pain, stretch, or temperature such as on the skin."
The ASCRS Textbook of Colon and Rectal Surgery: Second Edition (2011) - Pages 175-176
"The rectal epithelium is an absorptive tissue with a delicate simple columnar epithelium. In sharp contrast, the human vagina is lined by a multilayered stratified squamous epithelium designed for the strain that can occur during sexual intercourse and childbirth."
"Relative Safety of Sexual Lubricants for Rectal Intercourse." Sexually Transmitted Diseases. 2004 Jun; 31(6): 346-9. doi:10.1097/00007435-200406000-00005. (PMID 15167643)
"Anorectal infection and sepsis are common challenging problems. Although often used synonymously, sepsis and infection are different. Sepsis are the systemic responses to local infection, including hyperthermia, tachycardia, tachypnea, hypotension and altered mental status. Fortunately, most patients with infectious anorectal diseases present with a localized abscess or fistula, without systemic toxicity... Primary anorectal sepsis refers to bacterial invasion of the soft tissues in the peri-anal area..."https://www.ncbi.nlm.nih.gov/books/NBK6882/