Watched this match years ago, but forgot about that shot. Interesting that both Fels and Double J noticed the skid right away, and of course Engert’s reaction says he thought something strange happened. Nice slow motion replay at 1:25:48 with further commentary.
Side note, used to have a copy of Fels’ book Mastering Pool, but lost it sadly. Also, boy do I envy Rempe’s mechanics.
You can get a copy of his "Advanced Pool" which is an updated version of "Mastering Pool" with better diagrams for under $10 delivered to your house. No one pocket section, though. used.addall.com