The Doctor had taught River that nothing was inconsequential when observing others and their surroundings. Therefore, when Bill spoke of trying to forget something with the use of drinks, she meant to explore that a little further. Until he spoke again of angels.
This was definitely something worth noting. She looped her hand into the offered crook of his arm. He may have offered to be her escort in doing so, but she was firmly taking the lead, heading back inside the hotel. She was pretty sure she had passed some sort of lounge as she had hurried out to meet the Mr. No-Show.
"The angels I spoke of are called Weeping Angels. They are an alien race that appear to others as statues when they are seen. Yet when your back is turned, or your eyes are closed, or you even blink, they attack, sending you backward in time with a single touch, to feed on the residual energy."
River looked at Bill curiously. "But those aren't the kind of angels you are talking about, I'm guessing. What are your angels?" Heavens above, was he from a point in time that still believed in demons and angels?