system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:If the counterfeiter is talented enough to make a $100 bill that looks and feels like real money to a cashier, why aren't they talented enough to make it react the same way to the pen they use to test it as real money does? Is that pen truly a foolproof way to tell if a bill is real or fake?
gpt
The pen in not 100% effective. The reason we have multiple means of verification like the strip, the pen, and the watermark to make counterfeit bills harder to produce. I've had 5's washed out and printed over with a 100 that passed the pen but failed the watermark. Its possible to make very good fake bills but very hard to make perfect ones.