At the very end of the first episode, Airi is shown saying "Whose eyes are those eyes?" - a key phrase from Chaos;Head, another visual novel and anime from the same creators.
From what I've read, Robotics;Notes does have some ties to Chaos;Head that were seemingly cut from the anime completely (possibly copyright issues?). But it doesn't make sense to me that she would say this line when Chaos;Head is not referenced at all at any other point in the anime series, if I remember correctly.
Did I miss the meaning of the line within the anime series? Or does anyone have an explanation from the Robotics;Notes visual novel?