"Cover," whispered Cavor, and I turned towards the bushes.

At that instant came a thud like the thud of a gun, and then a thing
happened--it still haunts me in my dreams. I had turned my head to look
at Cavor's face, and thrust out my hand in front of me as I did so.
And my hand met nothing! I plunged suddenly into a bottomless hole!

My chest hit something hard, and I found myself with my chin on the edge
of an unfathomable abyss that had suddenly opened beneath me, my hand
extended stiffly into the void. The whole of that flat circular area was
no more than a gigantic lid, that was now sliding sideways from off the
pit it had covered into a slot prepared for it.

Had it not been for Cavor I think I should have remained rigid, hanging
over this margin and staring into the enormous gulf below, until at last
the edges of the slot scraped me off and hurled me into its depths. But
Cavor had not received the shock that had paralysed me. He had been a
little distance from the edge when the lid had first opened, and
perceiving the peril that held me helpless, gripped my legs and pulled me
backward. I came into a sitting position, crawled away from the edge for a
space on all fours, then staggered up and ran after him across the
thundering, quivering sheet of metal. It seemed to be swinging open with a
steadily accelerated velocity, and the bushes in front of me shifted
sideways as I ran.

I was none too soon. Cavor's back vanished amidst the bristling thicket,
and as I scrambled up after him, the monstrous valve came into its
position with a clang. For a long time we lay panting, not daring to
approach the pit.