> While this is technically an "s", the way it was written "ſ" can be confusing, as it is quite close to "f".

And when set in italics, it looks like the integral symbol: ſ (depending on your font, it may or may not have a descender)

In fact, this is where Leibniz got the idea for the integral symbol: it stood for ſumma, Latin for "sum".