I almost wonder if that cop was pulling your leg or else he was truly a dumb guy who hadn't had any drug training. All the police officers I know down here are trained to look at people's eyes and watch the subtle muscle movement changes that occur with the effects of cannabis, particularly as someone tries to track something visually (like the tip of a finger). For coke and meth, they can often tell by pupillary reaction along with behavioral changes. It's the same training they gave us as paramedics, and it didn't in any way involve looking in people's throats. Fortunately--or perhaps not so fortunately--not all cops are so dumb. If it makes you feel any better, most reasonably intelligent cops wish weed were legal, too, because they know it's nothing in comparison to other more dangerous drugs. Still, they're paid to enforce the laws that are on the books now.