Robert Silverberg 
Hot Night, Alien in Tree [EPUB ebook] 
A Short Story

An unsuspecting newlywed finds himself the subject of alien scientific study in this humorous tale from the Hugo and Nebula Award–winning author.   After an evening out to dinner, one sultry midsummer eve, Charlie finds himself in the right place at the wrong time: lying underneath an oak tree after making love with his new wife. But while Maria drifts off into dreamland, Charlie finds himself being watched by a one-eyed alien in the branches above.   No leering voyeur is this alien; it’s here on research purposes only and has been lucky to observe human copulation. Now it has a favor to ask of Charlie: a personal demonstration. To make the situation more palatable, it transforms into one of Charlie’s beautiful ex-girlfriends. To keep the alien’s eye from wandering to his sleeping wife, Charlie will have to make the ultimate sacrifice . . .