Exactly what my wife says. The experience isn't complete without his sperm in her - she enjoys it long after he's left. So do I. More than once, when she comes home after sex at her BF's place and we are in bed naked about to have sex, she'll ask me "how does it feel knowing I'm full of another man's sperm?" That's like a lightning rod to me - erects me fully, instantly and I can't wait to be in her. And sometimes she'll make me wait a couple of days and teases me about getting PG. It always gets me going.