Ehem....
"About 4 percent of women who deliver vaginally end up with a more serious tear in their perineum that extends to or through the rectum. This kind of tear can cause considerable pain for many months and increases your risk of anal incontinence.
These severe tears are called third- or fourth-degree lacerations. A third-degree laceration is a tear in the vaginal tissue, perineal skin, and perineal muscles that extends into the anal sphincter (the muscle that surrounds your anus). A fourth-degree tear goes through the anal sphincter and the tissue underneath it."
and the main attraction (NSFW NSFL) (you have to forward it a little to see "it")