the ruler drop

Ms Zhang was telling me to have a look at facial reflex actions but i'm not quite sure how I would test that. So far I'm just thinking that the ruler drop test would be my best bet. And since it's a quick experiment I don't think it would be smart to have 'time' as one of the variables, I thought 'distance (cm)' would be better. As in, how many cm have passed before the subject has grabbed the ruler