A childhood belief about aliens

As a girl, I read lots of books about UFOs (pretty much the same type I still like to read, secretly). And I loved to read in bed, but then, of course, the lights had to go out --
One of the bedroom windows was small and high, and the light fell on the wall right across from me. At one point, I noticed that the shadow wasn't of a tree's branches any more, but of an oval shape on a dark stalk. It looked like the shadow of E.T.'s head and long neck. I stared at it for hours, frozen in fear. It would sway back and forth; it would vanish abruptly, and rise slowly back into view. This happened night after night.

I was so sure this was an alien. What else could it be? What would cast a shadow like that, or move like that? Eventually, I lay there long enough to figure it out. The alien's body was a metal pod buried just beneath the soil in the garden. It withdrew its head in the morning, and extended its neck at night. The alien was an investigator, not harmful or very friendly, but there to study human beings. There was a forcefield around my house that kept it from getting in, but it watched at my window anyway. It could sense if I thought too much about it, and that was why it sometimes ducked out of sight.

Today -- and I mean literally today, it took me that long to figure it out! -- I'm pretty sure it was the distorted shadow of a streetlamp that used to stand a few yards away.