And, of course, higher denominations are subject to greater scrutiny.

I remember having a conversation with my mother where she recounted an experience of having a twenty dollar bill examined at a store, and wondering who on earth bothers counterfeiting twenties anyway. I said that if I were going to counterfeit money, that's the denomination I'd pick, because it's the largest bill that most people spend regularly and casually. Hardly anyone seriously examines them, so your chances of getting caught are that much smaller.