"They're probably watching me. Well, let them. Let them see what kind of a person I am. I'm not even going to swat that fly. I hope they are watching... they'll see. They'll see and they'll know, and they'll say, Why, she wouldn't even harm a fly."
- Psycho, 1960 Hitchcock film
I killed a fly and thought of the saying:
Es una mosquita muerta.
"Mosquita Muerta: is a person who pretends to be innocent, dainty, and weak (hence a dead fly), but they are actually evil backstabbers. Essentially a Spanish version of a - snake in the grass. They are extremely manipulative and will have everyone fooled by their game except for the smart ones. They will usually try to make the ones who don't fall for their game look like bad people while they play the victim."
- Urban Dictionary
