This is test footage from the classic scifi film Alien which shows Bolaji Badejo, the unknown star who played the xenomorph, getting a feel for how the creature should move.
The video still manages to be quite creepy, which I attribute to the fact that Bolaji put a lot of work into playing the role, going so far as to consult with H.R. Giger to make sure he moved properly while in costume.
Man, I miss the good old days of actors wearing badass latex suits, although I'm sure the actors don't miss the constant battle with heat exhaustion!
--via i09
What made the alien scary in the first films is the very fact that we didn't see it (or at least not completely) until the very end.
Still, interesting behind-the-scenes footage.