The circus has been John Thackery’s preferred metaphor for describing what goes on in the Knickerbocker hospital, but it wasn’t until this week’s The Knick that we finally got to see the dog and pony show. “They Capture the Heat” is a full-on carnival act compared to the rest of the season, featuring five medical emergencies, two family members in peril, gun totting thugs under the big top, an aborted abortion, and for the grand finale, Thack learning how to ride a bike. Put simply, tonight’s episode was kinda bananas.