When a person feels sexually aroused.
Here is a story for you horny girls ;)
Amanda thought about Zach. She got so horny thinking about Zach. She laid back in her bed and masturbated. After, she got up the guts to call her crush Zach tell him she was horny. He replied saying he will be there in 5 min. Amanda put on her best lacy black thong and bra. When he arrived she took him to her bedroom. They kissed while he slowly undid her size 36C bra and fondled her breasts. He flipped on top and kissed her nipples gently and massaged them, teasing her. She let out a faint moan. He responded by working his way to her mouth. Amanda, undid his boxers. Exposing his 9" rock hard dick. She slipped her soft lips over his cock and gave him a blow job, he came in her mouth and she swallowed every last bit. Zach then slowly slid off her thong. He flipped her over and kissed her stomach slowly working his way to her pussy. He saw her dripping wet pussy. He teasingly licked the tip of her clit. He let his tongue slip in and out of her pussy and just when she was about to orgasm, he slipped it out and climbed on top of her. He went in and out of her pussy very slowly. She flipped him over and straddled him on top. She bobbed faster and faster, up and down, on his long hard dick. She arched her back, moaning and purring with ecstasy. She wanted him to go deeper and deeper insider her. He finally hit her g-spot. And fell over with him on top of her curling her toes and let out a big moan. They orgasmed at the same time and he pulled out and came all over her stomach.