he group saw that a member of the conquered race was coming
along the street behind them. He was dressed all in brown--his hat, his
shirt, his pants.

The instructor put his hand on the butt of the _Thor_ gun.

The native walked past the group without seeming to see it. He was
whistling between his teeth. He walked on ahead of them, turned down an
alley, and disappeared. The instructor took his hand off the _Thor_ gun.

"He wasn't really following us; he wouldn't dare. Does anybody have any
questions?" He looked brightly around the group.

"Yes, I have," Joe Buckner said. "Why don't we just kill all of these
natives? They're not any good to us."

The instructor smiled slyly. "I'll tell you a little secret about that.
It's awfully hard to kill _all_ of any race. No matter how thoroughly
you do the job, a few always manage to escape. Then they breed and
increase in spite of everything you do.

"After we had conquered this planet we had trouble catching all of the
natives. They were the most cantankerous, persistent race you can
imagine. So these museums were set up, to lure them in here. We
announced that these places would be set aside and that they would not
be bothered as long as they remained in the museums. All in all, we made
the museums rather attractive places, hoping that--"

"I see the plan!" Joe Buckner said glowingly. "After you got them all
into the museums--_blooie!_--knock all of them off at once!"

The instructor smiled. He looked as pleased as if he had thought of the
idea himself. A little stir of applause ran through the group as they
expressed their gratitude to their rulers for making this world safe for
them.

"Why haven't they been killed before now?" Billy Kasker asked. "These
museums were opened over forty years ago. Surely--"

"I don't know about that," the instructor answered. "I think probably
our rulers are waiting for a propitious time, or perhaps for an incident
that will give them an excuse to carry out their plan."

"I hope they don't wait too long," Joe Buckner said. "Golly, I want to
be a _Thorgunner_ and get in on the mop-up when it comes!"

The group stirred, seemed to look forward to the day of the final
slaughter.

"Any other questions?" the instructor asked.

"I have one," Billy Kasker said hesitantly. "It doesn't exactly have
anything to do with our trip through the museum--it's something I ran
across in a book--but I don't quite understand it, and I wondered--"