Two astronauts land on Mars.
Their mission: to check whether there is oxygen on the planet.
"Give me the box of matches," says one. "Either it burns and there is
oxygen, or nothing happens."
He takes the box, and is ready to strike a match when, out of the blue, a
Martian appears waving all his arms...
"No, no, don't!"
The two guys look at each other, worried. Could there be an unknown
explosive gas on Mars?
Still, he takes another match... and... A crowd of hysterical Martians is
coming, all waving their arms: "No, no, don't do that!"
One of the astronauts says, "This looks serious. What are they afraid of?
Nonetheless, we're here for Science, to know if man can breathe on Mars."
So he strikes a match ‑‑ which flames up, burns down, and....NOTHING
So he turns to the Martians and asks, "Why did you want to prevent us from
striking a match?"
The leader of the Martians says, "It's Shabbos!"