Hi Rebis the mother Alien laid her eggs in people by way of the mouth. It kind of like used a human body as the host  and incubator for the baby alien. after a indeterminate time the egg would hatch then the thingi with the teeth explode it's way out of it's host via the chest.  I believe that was  how it worked. "Yuck, yuck, yuck, that was a really gory movie.  If you have week stomach and an empath, I don't recommend it.
Alien

Spectator
Posted on: March 10, 2008, 07:00:35 PM
Hi Rebis they exploded their way out of the chest I guess it would appear to be more gory then through the stomach I guess. Anyway to be sure it's all planed out by the guy who make the movies.  

 Wing Walker says it reminds her of a toothy penis.