Liam's anonymous blood donation to Sandoval. It had a chance of revealing who he was, and/or what he was. Liam also knows full well that Sandoval is, to put it mildly, not on the side of angels. However, add it to how little he acknowledges Ha'Gel unless absolutely necessary. Despite everything, Liam's donation says that he acknowledges Sandoval as his father, and loves him, despite the messy situation.