You might remember the scene in Prometheus when David wakes up the engineer from hypersleep.
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David utters a few words in his language, and the engineer proceeds to rip David’s head clean off…well not clean, there’s a bit of spine still attached and it’s pretty messy…
The engineer proceeds to kill everyone on the Prometheus team, except for Shaw, who escapes…
This scene is shocking because you expect a more advanced civilisation to act peacefully, especially during that sensitive first encounter. But nope, he just starts beating everyone to a pulp. He appeared to be disinterested in the reason for their presence and instantly took action to eliminate them as an obstacle for what he was about to do, which was to either destroy or invade Earth.