"We didn't know, for a long time. That was another thing we learned."

Hange shifts her gaze back to Sawney and Bean. If they were people, there's little evidence of anything left of them now.

"The humanoid forms... the fixation on eating humans above all other forms of life... I had my suspicions, but no proof. And how it happens is still confusing. The legend passed to me is that long ago, a human came into contact with a being known as 'the source of all life', and thereby became the first titan shifter. A human who consumed titan serum, purified from titan shifter's blood, becomes a pure blooded titan - mindless, like these. A pureblood titan becomes a titan shifter from devouring the spinal cord and cord blood of a titan shifter."