Ink Hearts determine whether or not a creation from the Ink Machine used to be person.

While the Ink Hearts have only to do with the "Alice" arc, I think they have a greater meaning. A non-person creation will have one, but a person-turned-creation does not.

Support for this theory:

•Humans have hearts inside them, making an Ink Heart unnecessary. All that changed about the humans were there appearances.

•"Alice" doesn't recognize them as if she has one. While hearts may be gross to some, she refers to them as "extra-thick ink."

•"Alice" calls Wally Franks' Boris the "perfect Boris" without ripping his heart out. She can tell he was human by his behavior.

•Franken-Boris disintegrated into ink upon defeat due to the Ink Hearts in him. He bleeds out unusually profusely. The fact that "Alice" had all those Ink Hearts at her disposal without much progress on making her look exactly like a perfect Alice Angel suggests she was really saving the Ink Hearts for the perfect Boris.

•"Alice" is slaughtered by Allison Angel without disintegration. This is unlike most creations Henry fights which have had Ink Hearts and disintegrate.

•Norman is killed without disintegration. This would confirm that he is human since all previously human characters that die do not disintegrate like those that potentially have Ink Hearts.

•Sammy Lawrence is killed by "Bendy" presumably. Even though it is off-screen, ot sounded more like a person getting killed than a common enemy being defeated.