Episode one concluded with Dolores Abernathy (a host) swatting and killing a fly on her neck. This was a significant ending, because the hosts are supposed to be incapable of killing or harming any living thing — flies included.
This is why we saw flies crawling uncomfortably close to the hosts' eyes earlier in the episode, and watched as Bernard assured the head of Quality Assurance that a host's "core code" was intact, which would meant it "literally couldn't hurt a fly."
If Dolores was able to kill the fly, it means that core code is beginning to splinter. What will that mean for the safety of the guests moving forward? We'll have to keep watching to find out.