It also makes f flat.

Explaining the joke: In standard Western music's 12-tone equal temperament scale, the pitch class E-natural is exactly the same as the pitch class F-flat. Putting it another way, look at an F key on a piano, flatten it by one semitone by moving left, and you get an E key.

At first your comment fell flat with me but then I realized it was pretty sharp. You are a natural.

But the cute proof was pretty cute. I recommend calc teachers try to work it into their lecture on e.