I tested this simply and summarily. Shutting my eyes for a second,
when I opened them she was gone. Shutting them again and opening,
there she was, sunning herself, breathing deep and long, watching her
own beauties as the light played with them. I tried this many times
and it did not fail me. I could, with her assistance, bring her upon
my retina or take her off it, as if I had worked a shutter across my
eyes. But as I watched her so I got very excited. Her business was so
mysterious, her pleasure in it so absorbing; she was visible and yet
secret; I was visible, and yet she could be ignorant of it. I got the
same throbbing sort of interest out of her as many and many a time I
have got since out of watching other wild creatures at their affairs,
crouching hidden where they could not discern me by any of their
senses. Few things enthral me more than that--and here I had my first
taste of it. I remember that my heart beat, I remember that I
trembled. Nothing could have torn me from the spot but what precisely
did, an alien intervention. The besotted Harkness stopped short in
his recital and asked me what I was staring at.

That was the end of it. I had rather have died than tell him. Perhaps
I was afraid of his mockery, perhaps I dared not risk his unbelief,
perhaps I felt ashamed that I had been prying, perhaps I grudged him
the sight of her moulded beauty and keen wild face. "What am I staring
at? Why, nothing," I said. I got up and put the strap of my school
satchel over my head. I never looked for her again before I walked
away. Whether she left when I left, whether she was really there or a
projection of my mind, whether my inner self, my prisoner, had seen
her, or my schoolboy self through his agency, whether it was a trick
of the senses, a dream, or the like I can't tell you. I only know that
I have now recalled exactly what I seemed to see, and that I have seen
her since--her or her co-mate--once or twice.