text: "What a brain!" Northrop chortled, squatting down closer. "Why doesn't it back up or turn around? It may be alive, but it certainly isn't very bright."
  The creature, now in the shadow of the 'Troncist's helmet, slowed down abruptly - - went limp -- collapsed.
  "Get out of his light!" Jack snapped, and pushed his friend violently away; and as the vicious sunlight struck it, the native revived and began to revolve as vigorously as before. "I've got a hunch. Sounds screwy -- never heard of such a thing -- but it acts like an energy-converter. Eats energy, raw and straight. No storage capacity -- on this world he wouldn't need it -- a few more seconds in the shade would probably have killed him, but there's no shade here. Therefore, he can't be dangerous."
  He reached out and touched the middle of the revolving shaft. Nothing happened. He turned it at right angles to the plate. The thing rolled away in a straight line, perfectly contented with the new direction. He recaptured it and stuck a test-prod lightly into the sand, just ahead of its shaft and just inside one paddle wheel. Around and around that slim wire the creature went: unable, it seemed, to escape from even such a simple trap; perfectly willing, it seemed, to spend all the rest of its life traversing that tiny circle.
  I don't usually put non-engineered animals in the index, but I couldn't resist. The fontema is a dead ringer for NASA's latest lunar robotic explorer - the Axel rover.