Don't fool around with something when you don't know what it is.
4 seconds sound clip from the The War of the Worlds (1953) movie soundboard.
You can hear this line at 00:15:33 in the DVD version of the movie.
Quote context
[...]
- Maybe these are not men. Not like us.
- Everything human doesn't have to look like you and me.
- If it's men from Mars, we ought to let them know we're friendly.
- Don't fool around with something when you don't know what it is.
- We'd be the first to make contact with them, see?
- We could show them we're friendly, huh? Uh, walk out there with a white flag.
- Here, I-I've got an old sugar sack in my car.
- What are we going to say to them?
[...]