And the second…
1. A slight, unreal, or superficial likeness or semblance.
2. An effigy, image, or representation.
Alphonse likes mirrors. Smooth, solid surfaces that reflect images he longs to see. As he slips off the red cloak and midnight leather, it's not hard for him to pretend the image in the mirror is not of himself, but of his brother undressing. His own mirrored appearance makes it easier for him to lean over the bathroom sink and glide his tongue over the smooth glass. The chill of the bathroom porcelain on his bare skin brings to mind the feel of cold, steel limbs. And when he reaches between his legs, taking himself in hand, he only needs to press close to the mirror to make the fantasy seem real.
Gasps and moans echo off the tiles, and it's almost as if there is more than one person. It never takes long for Al to come; a muffled cry escaping the lips that slipslide over the looking glass. He'll stay there, pressed against the chilly, polished metal until his breathing returns. When he finally opens his eyes, the apparition before him—of golden eyes, flaxen hair, and gleaming automail—fades, along with the after effects of his orgasm.
Al doesn't mind that the reflection becomes his own once more. Gone is the brother, gone is the lover, gone is the other, to where he cannot follow. All that remains is Alphonse, a mere reflection of Edward, and the reflection of Alphonse. Yet, the simulacrum only gives him more determination to seek the vision he truly wants to see.
So, I have a thing for mirror!sex (see my YGO fic, Distortion, if you don't believe me). XD