If you’ve ever been in a Parisian café, you’ve seen Heisenberg’s uncertainty principle at work. In this environment, waiters move about like errant electrons, brushing past you with little care for their momentum, their movements, or their duties. To a stationary observer, it is impossible to know both the location of a server and the speed at which he is ignoring you.
The croque-monsieur made its debut in 1910, in a café on the Boulevard des Capucines. The origins of the name are unknown, but I suspect the etymology is quintessentially French. An exasperated Frenchman …