Martians

Two astronauts land on Mars. Their mission is 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 his six 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? But 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
happens. 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!”