Damn Cookies... talk about grasping for straws... is there even the slightest chance you'll be able to see this movie in the theater with an open mind? Or are you gonna be one of those people in the theater that yells out "LAME" everytime the movie shows an Alien doing something that you don't think is possible? And one last thing... how much can an Alien lift with it's tail? Do you know what the stress limit is on the Alien's bone structure? For that matter... how much does a Predator weigh? You mentioned do the math... so I'm gonna take it one step further and give me concrete evidence, as displayed in the four Alien films and two Predator films. In your answer, stick to what has been revealed in the films with as little "assumption" as possible, please. Give me concrete answers to these questions (fact heavy and assumption light) and maybe some of us here will see what your doing as bringing up valid critiques/points rather than nit-picking for nit-pickings sake. Otherwise sit back and enjoy the ride the movie is gonna take you on. You'll end up enjoying the film a lot more if you stop trying to nit-pick. ;-)
As for the length of the Alien's tail in that Face-Off shot, I'll agree it appears to be a bit large, but that could be attributed to the camera angle and/or camera lens used to film the shot (it's a common cinemtography technique...)