Clitoris
During sexual arousal, erectile tissue fills with blood. This causes the clitoris to grow. It grows until orgasm happens. Also during arousal, touching the clitoris and other sensitive areas of the female genitals makes a woman's vagina change shape and release a lubricant.  The lubricant and change of shape makes it easier for a man to enter a woman and for sex to occur. Most of the clitoris is hidden inside the body. Only a small part of it is seen outside the body. Adding the outside and inside parts, the clitoris is about the same size as the penis. The clitoris and penis grow from the same tissue in the womb; they bear many similar parts.