There is a scientific distinction between having guts and having balls. I have heard distinguished colleagues (husbands, that is) use the two expressions interchangeably.
They both refer to courage, of course; but do they really know the difference between these two degrees of bravery?
Here is the official distinction; straight from the British Medical Journal: Volume 323; page 295.
HAVING GUTS
It is coming home late, after an evening out with the lads, being met by your wife with a broom, and having the guts to ask her: “Are you still cleaning, or are you about to fly somewhere?”
HAVING BALLS
It is coming home late after an evening out with the lads, reeking of perfume and beer, with lipstick on your collar, giving your wife a slap on the backside and having the balls to say: “You’re next, Chubby.”
I trust this clears up any confusion.
From a clinical standpoint, there is no difference in the outcome: in both cases the mortality rate is 100%.
NOTE:
My wife maintains that I am a shameless chauvinist.
I believe I have merely done my duty as a scientist of the soul in clarifying the obvious doubt that troubles many.