The true poison finger (paper tigers karate move explaned)

The movie paper tigers is about three men who used to be karate students, they find each other again when their sifu or master dies due to...poison fingers? Fingers are fingers, how can you poison someone if you use your fing-*skips ahead 15 minutes* *makes demented old man noise* what do you even by poison fingers...sorry. *sits back in chair* *clears throat* So um, can you cut that? Ok, so I think what is actually happening is, spinal cord severing. What I mean by that is spinal cord is wire, wire cut no heart movement. In more complicated speech, the move only work on the back in specific places. So, I think that would be the most logical answer since, oh I don't know, ALMOST EVERYONE IN THIS MOVIE WEARS EITHER SHIRTS (which are thin may I remind you) OR A THIN PIECE OF CLOTHING, like the thing the sifu wore, and since he was older (probably 60-70 possibly older) he probably didn't have much muscle or fat mass (based on how much we see of him fight the poison finger user), and most older people bruise easier, so all my observations point towards spinal cord severing. So if you hear of someone using "poison fingers", wear thicker clothes or put some sort padding on the spine. Or the guy could have just laced his fingers with poison...but that's probably not it. So, defend your back against a poison finger user, then the powerful move is rendered useless. But, watch the movie, it's good, you can watch it on Netflix.