Deep in space, an astronaut comes across a mysterious giant ball of metal and stone, bigger than a star. He goes for a spacewalk outside to get a closer look, when suddenly, the ball swallows up his spaceship whole.
Luckily, a minute or two later, some freindly aliens pass by and pick him up.
"Hey!" shouts the astronaut. "That thing just sucked up my ship!"
"Well of course," reply the aliens. "It's a Dyson sphere..."