Powerful oath of the scrotum

As a kid in the schoolyard, I remember making promises to do something, or making an oath to reinforce what I said was absolutely true. One went like this:

Cross my heart, and hope to die, stick a needle in my eye.” And if we got away with crossing our finger hidden behind our backs, our promise didn’t count as a real oath.

Somehow, these silly antics were supposed to reinforce the truth. As we get older and grow out of our elementary ways and methods of making what we say sound more believable, we’ve changed things up a little: “To be totally honest with you…” Well, as if what we just said was going to be more truthful than usual.

I just ran into a very strange saying in the Old Testament Bible. This one has always stumped me and caused me to ponder upon its meaning and how it originated. It seems that an oath made under a man’s scrotum was somehow more binding.

So the servant put his hand under the thigh of his master Abraham and swore an oath to him concerning this matter.” (Genesis 24:9)

Really stumps me. Hard to imagine its significance. Anyone get the meaning of this one or how it originated?!