As a parent, you do whatever you can to protect your child. You want him or her to make all the right decisions, as you know that going down the wrong path can lead to trouble in the future.
The police pull you over, claim to find illegal drugs in your car, and use a field test to examine them right there on the side of the road. The chemical -- cobalt thiocyanate -- starts out pink and then turns blue. That means, the police tell you, that the substance was cocaine. You're arrested immediately.