A desperate young husband phones the doctor

A determined younger husband telephones the physician: “

Physician, physician, my spouse and I are brown-haired whereas our son has crimson hair, how is that this doable?”

The physician thinks about it for a couple of seconds and then asks: “

How usually do you and your spouse have intercourse?”

Embarrassed, the younger man replies: “Yearly kind of…”
“Right here’s the reply!”

“Which means what?”
“The rust, it’s the fault of the rust!”