No spark on MS 460

[Hendog]

What am I doing wrong? I'm trying to check for spark on a MS 460 and can't seem to see any spark. I've also tried on several other saws that I use and will fire up every time, but when I try to check for spark, I see nothing. I remove the plug and reinsert it in the boot and then hold the boot with the threads of the plug grounded on the cylinder head. I've tried on 2 other saws that will run but done see the spark when checking it this way? What am I doing wrong to not ne able to see the spark especially on the running saws?