Cats copulate when a female enters her mating season and sends hormonal signals to nearby male felines that she is ready to breed. Female cats also make physical gestures to invite males to have sex, until a male finally mounts the female, penetrates her and bites her neck.
About.com explains that female cats often scream when the male retracts his penis, because it is barbed and may cause her pain. Female cats do not ovulate prior to conception like human women do. Rather, the act of sex with a male cat induces ovulation in a female; for this reason, it is not uncommon for female cats to give birth to kittens sired by multiple fathers.