i have a different take on the last couple shots. if you watch the trailer in slow-mo, starting at the picture where Darkness thinks Lex throws a spear at a Predator (i thought it was a tool, crowbar or something, sorry), i was under the belief that the Pred was racing to save the humans from an alien. the next few seconds show the uncloaked Pred sprinting full-tilt towards the humans (and they always seem to prefer to attack from a position of advantage, not a football-style tackle). it looks to me like the Pred tackled the alien somewhere just offscreen or else cut from the trailer. they roll around on the floor in the next few shots, the alien gets the pred on his back, and the pred jams his thumb claw into the aliens throat, as proved by the blood and painfully flailing tail. think its plausible that the Preds team up with and save the humans, like in the original comic, or just my wishful thinking?
