I kinda see where you're coming from, but just for clarity (because I get that the move doesn't work, but I don't understand why so it would be nice to know what precisely is the difference between the moves so it's easier to tell what will and won't work with certain abilities like Serene Grace, Sheer Force, etc, etc) what exactly is the difference between these two moves that do and don't work with Serene Grace?
For example, Body Slam (which does work with serene grace) has the following description:
http://www.serebii.net/attackdex-xy/bodyslam.shtml
but Poison Jab (which does not work with Serene Grace) has the following description:
http://www.serebii.net/attackdex-xy/poisonjab.shtml
and besides Poison Jab being useable in Sky Battle and Body Slam not being so, they're identical in terms of description (they even both have a 30% chance on inflicting their effects) so what is the difference between these two moves so you know what is and isn't a secondary effect?