for
lunch."

"Next time," said Keku firmly, "I'll take the Answerman watch, Mike. You
and this kraut are too lucky for me."

"If I lose any more to the Angel," von Liegnitz said calmly, "I will be
a very sour kraut. But right now, I'm quite hungry."

Mike prowled around the Power Section that afternoon with a worry
nagging at the back of his mind. He couldn't exactly put his finger on
what was bothering him, and he finally put it down to just plain nerves.

And then he began to feel something--physically.

Within thirty seconds after it began, long before most of the others had
noticed it, Mike the Angel recognized it for what it was. Half a minute
after that, everyone aboard could feel it.

A two-cycle-per-second beat note is inaudible to the human ear. If the
human tympanum can't wiggle any faster than that, the auditory nerves
refuse to transmit the message. The wiggle has to be three or four
octaves above that before the nerves will have anything to do with it.
But if the beat note has enough energy in it, a man doesn't have to hear
it--he can _feel_ it.

The bugs weren't all out of the _Brainchild_, by any means, and the men
knew it. She had taken a devil of a strain on the take-off, and
something was about due to weaken.

It was the external field around the hull that had decided to goof off
this time. It developed a nice, unpleasant two-cycle throb that
threatened to shake the ship apart. It built up rapidly and then leveled
off, giving everyone aboard the feeling that his lunch and his stomach
would soon part company.

The crew was used to it. They'd been on shakedown cruises before, and
they knew that on an interstellar vessel the word "shakedown" can have a
very literal meaning. The beat note wasn't dangerous, but it wasn't
pleasant, either.

Within five minutes everybody aboard had the galloping collywobbles and
the twittering jitters.

Mike and his power crew all knew what to do. They took their stations
and started to work. They had barely started when Captain Quill's voice
came over the intercom.

"Power Section, this is the bridge. How long before we stop this beat
note?"

"No way of telling, sir," said Mike, without taking his eyes off the
meter bank. "Check A-77," he muttered in an aside to Multhaus.

"Can you give me a prognosis?" persisted Quill.

Mike frowned. This wasn't like Black Bart. He knew what the prognosis
was as well as Mike did. "Actually, sir, there's no way of knowing