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Hindsight is the tenth episode of the ninth season of ER, and the one hundred ninetieth episode overall.
Guest Stars: Michael Ealy (Rick Kendrick), Eugene Lazarev, Abraham Benrubi (Jerry), Laura Ceron (Chuny), Troy Evans (Frank), Lily Mariye (Lily), Monte Russell (Zadro), Gedde Watanabe (Yosh), Thomas F. Duffy, Brittney Lee Harvey (Hockey Player), Scott Jaeck (Dr. Steve Flint), John Kapelos, Ana Ortiz (Laura), Vladimir Skomarovsky, Michael Spound, Leslie Bibb (Erin Harkins), Lynn A. Henderson (Olbes), Nynno Ahli (Security Guard), Nicole Bush (Mom), Mike Colter (Watts), Bill Forbes (Elf), Kirk Graves (Christmas Caroller #2), Daniel Hansen (Dwayne), Nels Lennarson (Angel), Hope Levy (Christmas Caroller #3), Jason Lieberman (Elf #2), Tomiko Martinez (Sedgewick), Stuart McLean (Tech), Patrick Roman Miller (Wiseman), Frank Noon (Birch), Bart Petty (McGiver), Julie Pop (Hannah), Paul Renteria (Custodian), Brent Roam (Herrero), Bret Shefter (Christmas Caroller #2), Lisa Stanley (Christmas Caroller #1)
The past 24 hours of Luka's day are shown in reverse after getting into a car accident with medical student Harkins after he worked the day after a staff Christmas party hungover; due to him being hungover, Luka misdiagnoses a 19-year-old boy with leukemia that end up leaving him brain-damaged.