Students are notorious for just skimming instructions, so teachers are known to hide an instruction that directs the student to do something silly. If the student includes that silly thing in their answer, that means they thoroughly read all the directions. If they did not include that silly thing, that is proof that at best, they just skimmed the instructions.
Saying "I failed these students because I instructed them to do something and they did it" doesn't quite seem like the right way to attempt to fight this. That seems like it would net a lot of false positives from students who aren't sure exactly what sort of games the teacher is trying to play.