This article is from the Alien Movies FAQ, by Darryll Hobsonand Eelko de Vos E.W.C.deVos@TWI.TUDelft.NL with numerous contributions by others.
- The alien could work like a battery, using electricity for it's energy
(suggested by the acid blood). This idea is suggested by the RPG.
- The alien increases its mass greatly between its chestburster and full-grown
stages of development. In order to do this it MUST eat something solid
(perhaps: flesh, minerals, metals)
- H.R. Giger introduces the concept of a bio-mechanical species (notice how
the Space Jockey of "ALIEN" was attached to/part of the machinery it was
sitting at?) If the aliens are part of Giger's bio-mechanical world then
it's entirely possible that they could eat metal alloys to increase their
mass.
- In an old draft of the "ALIEN" script, when Ripley finds Dallas cocooned
and the Brett-egg, she says to Dallas, "I'm going to get you out of here"
and Dallas replies, "No, it's too late for me, the alien has eaten to much
of me already... see what it did to Brett?"
- An Alien, like a fly, could "eat" by dissolving it's food with an acid
like substance, then eating the "soup" left behind. In this way, the alien
could eat pretty much any material (even metal).
 
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