Black Goo Inconsistencies (Major Spoilers)

At the beginning of the film we see the sacrificial Engineer drink the black goo which immediately breaks down his cells leading to the first elements of DNA for human life on earth. Later on, when David spikes Holloway’s drink with a tiny amount of black goo, Holloway appears to follow the same pattern of cell breakdown as the sacrificial Engineer, only at a slower rate; presumably because he only ingested a small amount. The inconsistency occurs when the mealworm bathes in the same black goo. This time, the goo mutates the worm into a "cobra-hugger". Also, when Fifield falls into the goo, he later returns as a super strong mutated version of himself. So, why do we see very different results from interaction with the same black goo? I am, of course, assuming that all of the above characters and creatures have interacted with same substance. Or, maybe the goo needs to mix with another substance; or be at a certain temperature to produce a growth effect rather than a breakdown. Thoughts???