-Why does David infect Holloway for no reason?
Before David infects Holloway he has a conversation with Weyland who is in cryo. When David leaves he comes upon Vickers lurking in the corridors. She askes David what Weyland said. "He said to try harder" he tells her.
Weyland wants to find out what the "black goo" is capable of without being the guinea pig. Could it make him immortal? Could it make him morph into an alien? Could it give him the runs? He tells David to infect someone. David picks the person he likes the least of the crew.