Have you got any better ideas for a subtle way of testing a drink? A finger is a lot more discreet than a paper strip. Try explaining why you are dipping a paper strip into your drink without accusing the guy of being a rapist. Slipping your finger in the drink is much less noticeable and almost no one will question it. This can be casually done many ways, for instance sticking your index finger in the glass while grabbing around the brim (not uncommon). The idea of the nail polish, applied before going out, is that it gives a woman a discreet way to test her drink. If it tests positive she can then covertly escape without alerting the guy that she found him out.