A variety of physiological changes and psychological reactions that accompany lovemaking, including intercourse. In the female, characterized by the vagina becoming lubricated, the barrel darkens in color, the inner two-thirds of the barrel increases in length and width, the clitoris becomes erect and increases in diameter. A sex hush may also occur. In the male, the most apparent characteristic is penile erection. Some may experience a sex hush. There is vasocongestion of the scrotum, and the testicles are drawn closer to the body. Both males and females experience an increase in pulse rate and an increase in blood pressure and deeper respiration. Sexual arousal culminates in orgasm. There are four basic phases to: 1. excitement phase, characterized by vasocongestion of the genitals and breasts, vaginal lubrication, rapid breathing, increased pulse rate, and other physiological changes; 2. the plateau phase, characterized by maintenance of sexual arousal and building of excitement; 3. the orgasmic phase, characterized by muscle spasms (ejaculation in the male) and an increase in the rate of breathing and a rise in blood pressure; 4. the resolution phase, characterized by a gradual return to the pre-excitement phase of sexual arousal. There is refractory period in males following orgasm in which it is difficult for further stimulation to result in heightened arousal.