"Parasite" in Holloway's Eye

Well, it could be hallucination. Holloway felt bad and awakened. May be there was no parasite at all in his eye. Only personal perception of Holloway. And if the parasite was... We know so little about the nature of the black liquid. Did you noticed the worms ander the soles of the scientists? Perhaps they were of the same breed.

Well, I think that those sequence of events encapulates David's words perfectly. When investigating the pod he states "Big things have small beginnings". Just a small drop of this black fluid infecting Holloway, perhaps changing his DNA enough by that time to have passed it on to Shaw, Shaw's "baby", it's growth and ultimate inpregnating of the Engineer...proto-xeno...etc. Obviously this proto-xeno is a glimpse of what we already have seen. ergo, small drop = big future for our favorite beasties. At least that's how my mind saw it. It appeared that whatever this parasite was, was doing to Holloway exactly what it did to the Engineer at the beginning, killing him slowly to change his DNA into something new. Perhaps a similar thing that was happening to Fifield.

According to VFXFuel it's an infestation