Mark Greene tells Dave Malucci that he used to play hockey in college. However, in Season 2, episode 12 " True Lies", he goes skating with his daughter and Susan Lewis and they have him barely being able to skate at all. This is common in a series that runs many years to tweak a character's info to suit the current storyline. These are the fun details that longtime fans start to find.
When Cleo is talking to Benton about him finding a job, she's wearing an Indiana Pacers shirt. The actress is herself a born-and-raised Hoosier and a basketball fan.
Luka and Abby go on their first date in this episode. It ends in tragedy.