What can be measured but not seen?

Wife: "Would you get a girlfriend again if I died?"

Husband: "Of course not."

Wife: "Why not? Don't you like being married?"

Husband: "Ok, I would marry again." (annoyed)

Wife: "Oh..." (sad)

Husband: -silence-

Wife: "Would you live in our house?"

Husband: "Sure, it's a great house."

Wife: "Would you two sleep in our bed?"

Husband: "Where else would we sleep?"

Wife: "Would you let her drive my car?"

Husband: "I guess I would, it's almost new."

Wife: "Would she use my golf clubs, too?"

Husband: "No, she's left handed."

Wife: -silence-