Coitus Interruptus: A contraceptive method whereby coitus is purposely interrupted in order to prevent EJACULATION of SEMEN into the VAGINA.Masturbation: Sexual stimulation or gratification of the self.Coitus: The sexual union of a male and a female, a term used for human only.Copulation: Sexual union of a male and a female in non-human species.Nephropidae: Family of large marine CRUSTACEA, in the order DECAPODA. These are called clawed lobsters because they bear pincers on the first three pairs of legs. The American lobster and Cape lobster in the genus Homarus are commonly used for food.Palinuridae: A family of marine CRUSTACEA, in the order DECAPODA, comprising the clawless lobsters. They are found in tropical and subtropical waters and characterized by short spines along the length of the tail and body.Hedgehog Proteins: A family of intercellular signaling proteins that play and important role in regulating the development of many TISSUES and organs. Their name derives from the observation of a hedgehog-like appearance in DROSOPHILA embryos with genetic mutations that block their action.Labor Onset: The beginning of true OBSTETRIC LABOR which is characterized by the cyclic uterine contractions of increasing frequency, duration, and strength causing CERVICAL DILATATION to begin (LABOR STAGE, FIRST ).