ha ha, you will know if you've ever given one to a girl before, she should get real stiff and clench something real hard like her legs together or her fingers may dig in real hard, her hips will start rolling and gyrating, she probably will not be able to speak so well if at all, you should feel a warm wash over your genitals as her fluids release, its a clear liquid. she should be super lubricated after she orgasms.