I did neither; I stood still.  I could see the thing with a fair amount of distinctness and forced my brain to take the record of my eyes.  But I could make nothing of it.

I guessed at rather than saw a hideous head rolling from side to side at the end of a long and sinuous neck, and writhing, reptilian coils lashing the rock at the edge of the water, like the tentacles of an octopus, only many times larger.  The body itself was larger than that of any animal I had ever seen, and blacker even than the darkness.

Suddenly the huge mass began to move slowly backward.  The sharpness of the odor had ceased with the opening of the eyes, which did not reappear.  I could dimly see its huge legs slowly rise and recede and again meet the ground.  Soon the thing was barely discernible.

I took a step forward as though to follow; but the strength of the current warned me of the danger of proceeding farther, and, besides, I feared every moment to see the lids again raised from the terrible eyes.  The thought attacked my brain with horror, and I turned and fled in a sudden panic to the rear, calling to Harry and Desiree.

They met me at the edge of the stream, and their eyes told me that they read in my face what had happened, though they had seen nothing.

“You—­you saw it—­” Harry stammered.

I nodded, scarcely able to speak.

“Then—­perhaps now—­”

“Yes,” I interposed.  “Let’s get out of here.  It’s horrible.  And yet how can we go?  I can hardly stand.”

But Harry was now the one who argued for delay, saying that our retreat was the safest place we could find, and that we should wait at least until I had had time to recover from the strain of the last half-hour.  Realizing that in my weakened condition I would be a hindrance to them rather than a help, I consented.  Besides, if the thing reappeared I could avoid it as Harry and Desiree had done.

“What is it?” Harry asked presently.

We were sitting side by side, well up against the wall.  It was an abrupt question, with no apparent pertinence, but I understood.

“Heaven knows!” I answered shortly.  I was none too pleased with myself.

“But it must be something.  Is it an animal?”

“Do you remember,” I asked by way of answer, “a treatise of Aristotle concerning which we had a discussion one day?  Its subject was the hypnotic power possessed by the eyes of certain reptiles.  I laughed the idea to scorn; you maintained that it was possible.  Well, I agree with you; and I’d like to have about a dozen of our modern skeptical scientists in this cave with me for about five minutes.”

“But what is it?  A reptile!” Harry exclaimed.  “The thing is as big as a house!”

“Well, and why not?  I should guess that it is about thirty feet in height and forty or fifty in length.  There have been species, now extinct, several times as large.”