I think it's all about the hands right after impact,...
(for right handed playes) If the palm of your right hand is facing up at this moment,... look out, righty slicy,...
If you can get it to where the palm is not facing up after impact the ball will go straighter and may even turn over just bit,... then you'll be fighting the dreaded lefty's,... The timing here is critical,... the hands have to roll over at impact, to quick left hook,... not quick enough, righty slicy,...
scuba