There's a lot of homework to be done here but this is how it works. Slusho, the drink that Jason has on his t-shirt, has the parasite eggs in it, unknowingly placed in the drink as part of the flavor, and that is what attracts "Cloverfield" the creature to Manhattan. He eats the parasite eggs. Hence the reason why Marlena, et al were infected with the eggs so that the monster could eat the eggs, or to produce more parasites for the monster to eat. Earlier when they are attacked in the subway tunnel, Hud says that he thought the parasites were just trying to drag him away. The parasites were trying to drag him away because he drank a lot of slusho, and therefore had the eggs inside of him. The reason we see part of Hud's body after the monster attacks him is because the monster sucks the parasite eggs out of Hud's body, (assuming that Hud drank a lot of slusho, "You Can't Just Have Six" (because assumingly, after six the parasite eggs start to infest in your system.) and left the carcass behind because he wasn't interested in the flesh, just the parasite eggs.

Interestingly enough, the company that Rob has been promoted to Vice President in is called Tagruato. The company that ironically enough, produces Slusho, among other things. So therefore, we awoke the monster Cloverfield from his slumber deep beneath the ocean, because we drank enough of this slushy drink containing as one of the ingredients, parasite eggs.

This is also why people such as Marlena were overlooked by the monster because apparently they never drank Slusho, and therefore didn't have any of the parasitic eggs in their system to interest the monster in the first place. Otherwise she would have been sucked dry just as everyone else had been in her first encounter with the monster.

Man I've done way too much homework on this flick, but the viral marketing compaign is fascinating.