I think the Colonel put St. John's Wort in his blend of 11 herbs and spices.
Think about it. Everyone loves some KFC. Everyone.
And why 11? Seriously. Who picks 11 herbs and spices? Everyone else would stop at 10. The eleventh spice is the key; the secret ingredient.
And really, why do you need 10 different herbs and spices, for that matter? Obviously to cover up the taste of the bad tasting secret ingredient, herb/spice #11.
So you eat the chicken with the St. John's Wort. You feel naturally happier. You are inclined to return and eat the chicken again. Instant repeat business.
I would be very surprised if this is not true.