Early in the book, the men guarding the posts have been seeing something in the shadows. It turns out to be a puppy, which is brought up to the fire and given something to chew on. It's a nice little moment that shows how, depsite the generally terrible situation humanity is in, there is still some kindness in the metro.
In 2034, when Sasha remembers that her and her father's exile from their home station when she was a young girl, it is mentioned that one of the guards tried to cheer her up and distract her from the situation with a shadow puppet show. It doesn't work, but he really tried to make her smile.
Also in 2034, Homer's quest to write an epic for the Metro in the style of the epic poems of old (hence his nickname) is pretty heartwarming. Homer is one of the few men who still believes that there's good in humanity, and hopes that his epic will detail the great deeds of the men of his era.