Dr Shaw

has the foreign body removed from her body and leaves it in the medical room.

Later, at the end of movie, she revisits the room and

the alien has grown about ten times the size, with no obvious access to food or energy.

How did it grow so fast?

  • 2
    Pretty common in sci-fi movies. Everything grows rapidly without sufficient food to do so. Commented Jul 5, 2012 at 11:12
  • 4
    Loss of density? ( Balloon alien! =D )
    – Izkata
    Commented Jul 5, 2012 at 12:36
  • Related: scifi.stackexchange.com/q/6282/1234
    – Xantec
    Commented Jul 5, 2012 at 13:14

3 Answers 3


The creature was trapped in a fully-equipped automated medical suite, which was clearly intended to keep a certain elderly man alive for as long as possible. In order to achieve that goal, it would need to be able to perform any sort of surgery - and probably, the most likely sort of surgery would be organ transplantation.

So, that means there must have been at least two other things in the room, besides fun-sized painkillers and a guys-only autodoc: blood (or some futuristic substitute), and replacement organs. Given the age of the intended patient, I wouldn't be surprised if there were muscle and bone grafts available as well. Some blood would have been readily available from the operating chair itself - since if a patient starts bleeding out you want to have a transfusion available immediately - and the organs would have been in cold storage somewhere nearby.

There was probably enough biological material available in that room to rebuild a person three or four times over if necessary, and all the creature would have had to do is bang open walls until it found the stuff.

  • 3
    none of that stuff was displayed anywhere though, the movie could just have shown it drinking a pint of blood or eating a table. Heck it was trapped last we saw it, couldn't even get out of claw. Then in the next scene its a giant squid. Reminded me of Akira. Commented Jul 5, 2012 at 16:16
  • 6
    @NimChimpsky The answer based strictly on the movie and nothing else is "it grew because that's what happened in the movie". That's not a very fun answer though, so I went with one that makes sense based on what we know about the characters and their environment.
    – Tacroy
    Commented Jul 5, 2012 at 17:14

That is something not really disclosed in the films. The aliens are genetically wired to grow large and fast, like in Alien where Parker was telling the others:

"It was like a man it was - it was ... big -"

It is one of the reasons they are so dangerous, they seem to lack a child phase and go from babies to adults within a couple of hours or maybe less.

  • 3
    so the apparent change in mass is not explained, they just generate it - defying the laws of physics. Othwise the giant facehugger at end must weigh the same as foetus thing. or have super efficent muscles. Why not just show it eating some tables or something. Commented Jul 5, 2012 at 12:52
  • 2
    Pretty much, the same is true for the massive amount of drool they generate. They do not eat people (that the films have shown) and it is not clear whether they eat 'human' food. There are all kinds of theories (some more plausible than others) but there are no concrete in-universe explanations.
    – Stefan
    Commented Jul 5, 2012 at 12:56
  • Also have a look at the 'How fast does an alien grow in the Alien movies' question
    – Stefan
    Commented Jul 5, 2012 at 12:56

Cells may have cavities filled in with mostly water (vacuoles). They allow cells (so the whole organism) to become much larger feeding mostly on water, with no other food. Plant seedlings grow from the seeds this way during the early stages of germination.

Vacuoles are common in plants but can be found in the Earth animals and protists, while this is much less usual. We do not know the biology of the creature. If the water was available in some pipe or tap inside medical room (quite probable), maybe this has been enough.

This does not explain the exact reason in the movie, just wanted to point out that fast growth need not contradict the logic or reality.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.