This is one weird film, concerned primarily with the twinned human drives towards religion and procreation, which here become one.
Fenix (Jodorowsky) is a child mime artist at a small Mexican circus. His mother Concha (Guerra) is a religious zealot whom we first encounter at the start of the film presiding in red nun-like robes over a shrine to a supposed saint who achieved that status by having her arms chopped off during a rape attack, being left to die in a pool of blood. Concha and her sister nuns' shrine contains a swimming pool full of the supposed "holy blood" (the Santa Sangre of the title), but that doesn't stop the bulldozers moving in and demolishing the site.
Concha, however, also works at the circus as a trapeze artist and is fired up by a hysterical if repressed sexual passion for the fat knife thrower Orgo (Stockweil) who carries on a provocative relationship both in and out of the ring with the blade-licking Tattooed Lady (Tixou). Fenix witnesses Orgo having sex with both the Tattooed Lady and his mother and then has to come to terms with something even worse. Life imitates religious idolatry when Orgo, surprised during an assignation with the Tattooed Lady, chops off Concha's arms before killing himself. A long spell in the asylum later, and the grown-up Fenix has rejoined his mother. On stage, he partners her in a bizarre routine which involves him standing behind her playing her "magic hands", while off stage he's become her grotesque helper-slave, having to do everything from the banal to the outright diabolical.
Santa Sangre draws heavily and with commendably lurid enthusiasm on the horror movie's obsession with the macabre rituals which make extravagant spectacle of death and suffering. It also addresses the perennial theme of the passive but tormented victim-killer completely under the thrall of a sadistic controlling force. In addition, there's a further weight of horror history in the film, with explicit reference to everything from Todd Browning's Freaks to Michael Powell's Peeping Tom.