SPOILER: Ella?
What was up with the hand thing? I've read that the Sonderkommando weren't allowed to interact with the female prisoners, so Ella might have just needed the physical contact on a human level.
But the way the camera held on her face, and the way her face seemed to betray that she was holding back an emotional response...
In a Hollywood film, this would 100% indicate that she and Saul had a history. As it is, it's ambiguous. Are we given any other clues?