Rapid breathing

Our breath when resting is a very peaceful and tranquil movement of air in and out of our lungs. It has the delightful title of "inspiration" for breathing in, and "expiration" for breathing out. When a woman is turned on, however, this breath comes in urgent puffs and probably has some involuntary moans escape with it as the air is forced quickly past her vocal cords. The increase in heart rate when her body prepares for orgasm means her internal organs and muscles are demanding more oxygen. If you can hear her breath change, youre on the right track. If you can feel her heart thumping, youre well on your way. This is her sexual body language giving you signals that she's aroused. However, if she's breathing normally after having her "big orgasm," perhaps shes a big faker.  

General writhing around and body movement

If your girl is curling her toes and writhing against you, chances are she's probably enjoying herself. Grinding and pushing against you means that she's really getting into it. If she's lying there limp, then things probably arent happening for her. Try changing positions, or stop entering her and warm her up from the beginning with your mouth or hands and see how her sexual body language progresses from there.

Thrusting hips

When she meets your thrusts, youre doing something right. It's pretty safe to say that if she's matching your body movements and is in time with you, then she's getting something out of it. Good sex is often very synchronized, as that is how our bodies are designed to produce orgasm; repeated movements in the right spot build to a climaxing. The trouble is finding the right spot, of which there are many. If she isnt meeting your thrusts then her sexual body language is telling you that she wants something else, so change positions and see how she responds.

Arms splayed out

If she's holding herself close she may not be feeling wild abandon -- her arms may be around you, her hands may be on your chest, above your head, wherever, except they're being held in close to her own body. If she's on top she may need her arms to maneuver herself and give herself some leverage to get the best angle. This is certainly not a definitive gesture, but can be useful. Her body should be responding to the situation at hand. She shouldn't be worried about covering herself up or where her arms are. If her arms are stretched wide, either held out to the side or splayed out on the bed sheets, you can bet her sexual body language is telling you you're right where you need to be and she's comfortable (and enjoying the ride).   

Vaginal muscle movement

You have one of your most sensitive parts inside one of her most sensitive parts -- with each movement inside of her you can feel the walls of her vagina, the muscles and flesh. The vaginal wall is an incredibly strong muscle and she will probably use this to some extent for her own pleasure during sex. You may also feel the contracting and relaxing during orgasm -- her vagina spasms and this will clench you to some degree -- but not always, so dont use that as a benchmark. Some women do have great control, and those who do are likely to have better sex and orgasms in general. If you dont feel any clenching, dont panic. You may know already by the feel of her vagina when she's not far away from orgasm -- she may let you enter further, or the overall sensation may be "just right" for you both. Only you can tell, so pay careful attention to her sexual body language and whats going on inside of her.