A woman who is sexually aroused will have hardened nipples and will probably be breathing heavy. Her legs will edge apart and her labia (vaginal lips) will become engorged. The womans clitoris, a hard button-like feature, will perhaps throb and be much more accessible.

She will most likely secrete fluid inside the vaginal walls and at the entry way. The vagina itself will seem to become larger as blood rushes to the region. (Note: blood also rushes to the breasts, causing them to swell and the areolas to become hard.)

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Interestingly enough, however, right before orgasm the clitoris shrinks a bit and nearly hides inside the vagina. This is an autonomic response and goes unnoticed by the woman.
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When orgasm begins, the interior vaginal muscles will contract, occurring in 10-second intervals (roughly). Each contraction lasts for a few seconds. Some are stronger than others and contractions can extend to the anus and uterus as well.

The skin will be flushed on the females body and her breathing will become even more shallow. She may pant and/or moan. Contractions will heighten to the point where they seem to come one right after the other. The interval between them will shorten as well and the woman may ejaculate at this point.

Muscles throughout the body may also contract and the woman will feel an immense sense of release. It is not unusual for a female to cry at or right after the moment of climax. The face may look as if she is in pain during the height of her pleasure, and theres no need to be alarmed if the body goes rigid for a few brief seconds.

It is completely natural and normal.