"What is it?" Xelia asked again.

"An Acruxian pet," Manning said. "It's native to Acrux and every Acruxian has at least one for a pet. Normally, they fill themselves with just enough air to float around. But if they're removed from Acrux, they become ravenous for air.[8] Only they can't suck up enough unless they find some sort of container with a hole about the size of its mouth. I guess these modern, air-tight rooms are perfect for them."

[8] The Heliumitis Acruxa is a small animal indigenous to the planets in the system of Acrux. It is a very simple organism, deriving all of its nourishment from air. Normally it keeps itself inflated to about a foot in diameter, constantly drawing in enough air to feed itself and to maintain that size. But if it is removed from Acrux, it immediately becomes obsessed with the desire to return and spends all of its time trying to obtain enough air to increase its size to the point where it can escape the gravity of whatever planet it is on. One Heliumitis has been known to create a complete vacuum in a space ship within a period of three hours and the destruction of at least one ship and its entire crew is known to have been so caused. In the early days, when Acrux was first discovered, a number of these creatures were taken to Terra. Immediately afterward there was an epidemic of flat tires on surface-cars and it was two weeks before it was discovered that the damage was due to the animals. Since that time, their possession has been outlawed on Terra, although in every other respect they are harmless.

"A pet?" Xelia said. He shivered. "That's not my idea of a pet. It could have killed us."

"I think that was the idea," Manning said. He bounced the Heliumitis on the floor like a basketball and caught it. "This, however, is about the only circumstance under which it would try to kill us, so we shouldn't blame it too much."

"Dtilla or Velmar Shonda?"

"Maybe both. No—it couldn't have been Velmar. The door was open when she left and remained open until you arrived. Besides," he added dryly, "she couldn't have been carrying it. She had no place of concealment this large. It must have been Dtilla or one of his friends. Probably hid on this floor, maybe in another room, and waited until we were in here. And that's probably the explanation of Chaun Cla. He was giving somebody the chance to sneak up here in advance."

"What about that thing?" asked Xelia, indicating the ball. "Hadn't we better turn it over to Central 

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