Spraying house-flies with lens cleaner - what is going on?

Factual Questions
21

I got two of the sons-of-bitches got in the house today, with blasts of Windex. Took one down in mid-air, too. Win, Win!

22

Ever tried spraying mouthwash at them? I hear it burns if you get them in the eyes, even if you think it’s lens cleaner.