It was God in the year dot
A few days after finishing His creations, the Lord called to Adam and said, "It is time for you and Eve to begin the process of populating the earth so I want you to kiss her."
Adam was a bit confused. "Yes Lord, but what is a kiss?" So the Lord gave a brief description to Adam who took Eve by the hand and took her to a nearby bush. A few minutes later, Adam emerged and said, "Thank you Lord. That was enjoyable."
The Lord replied, "Yes Adam, I thought you might enjoy that and now I'd like you to caress Eve." And Adam said, "What is a caress?” So the Lord again gave Adam a brief description and Adam went behind the bush with Eve.
A while later, Adam returned, smiling, and said, "Lord, that was even better than the kiss." And the Lord said, "You've done well, Adam. Now I want you to make love to Eve." And Adam asked, "What is 'make love' Lord?"' So the Lord again gave Adam directions and Adam went again to Eve behind the bush, but this time he reappeared in two seconds.
Adam said, "Lord, what is a headache?"