I have to say - last nights episode of LOST was incredible. The back story for Eco was moving and is the second best one I've seen yet. (My favorite is with Locke and his father.) And just when I thought that there wouldn't be any movement on the main plot... Bam - we have the Beast. (The big monster. Whatever. I prefer Beast.) I have to say that it was incredible. One of the things that show has done well is make excellent use of sound, and the Beast was no exception. It was like a lion - or some other cat-based predator, but "hyped" up as if from a nightmare.
I'm a bit confused as to what it could actually be. As I've stated before, my main theory is that the manifestations on the island are psychic based. However - the sound of the Beast was very mechanical, at least to me. But the only thing I can imagine that would resemble smoke would be nano-bots, and that just doesn't seem like it would fit - especially with the age of the island. (Sorry, not the island itself, but the time frame of the experiments.)
One thing to note - the Beast definitely doesn't seem to attack if you show no fear. Both Locke and Eco were able to stare it down. My wife seems to think it is a defense mechanism. But I can't imagine why a defense mechanism would ignore someone who shows know fear.
It appears as if next week we get to see the Other's camp, so maybe we will be able to glean a bit more information.