After wading into Maeve's in-game conspiracy and Bernard's quest to unlock wiped memories, "The Well-Tempered Clavier" picks back up with Dolores and William, now the playthings of Logan, the Westworld equivalent of Sid from Toy Story. With William's affection for Dolores grating on his nerves (somewhat fairly -- the guy is supposed to marry Logan's sister), Logan slices the female host to reveal her motorized innards and stomp on his pal's rose-colored glasses. Dolores shrieks, her fake blood oozes out of the wound, and Logan reminds William and the audience that she's just a machine.
The act of violence leaned in to another theory: Many believe that whatever William experiences in the park shapes him into Ed Harris's vindictive Man in Black character. A smaller contingent (like, very small) wonders if it's Logan who claws his way back to the park all those years later, not William. In episode five, MiB tells Teddy, "When this place started, I opened one of you up once. A million little perfect pieces." Maybe Logan slicing Dolores is the moment the MiB is referring to? Or maybe it's just a red herring so you don't think twice about where Dolores goes next.