It's a real question Franc. I noticed the difference today while cleaning the back side of the rim.
I couldn't figure out why there was a different design to just one spoke.
I didn't have the rear wheels off yet, but all the spokes felt the same when I checked.
The difference is at the very bottom of the spoke where it meets the rim.
If you reach around behind it you can easily feel the abnormality with your finger. (Did I just say that?)