Trivia: Staff Sergeant Collier's nickname, "War Daddy" is based on the nickname of real World War 2 Sherman tank commander Staff Sergeant Lafayette G. Pool, who fought with the 3rd Armored Division. Pool survived the war (though he lost a leg from his last combat operation) and died in 1991.
Trivia: Michael Pena, who played Gordo, actually learned how to drive the vintage Sherman tank that was used in the film.
Trivia: Actor Shia LeBeouf, a dedicated method actor who attempts to 'become' his role, avoided bathing for weeks before shooting. The actor had a dentist in Mexico pull a tooth before filming, and cut himself on set several times so he could display realistic wounds for the camera.
Trivia: The sound effects of high-velocity shells are created by the sound of spinning Frisbees taped with whistles mixed with sound of real shell pass-by.
Answer: Gordo was making a point to Norman that the crew of the "Fury" had seen some horrible things during the Battle of the Falaise Pocket. After wiping out an entire German army there, they were tasked with putting wounded horses out of their misery. The point was that Norman was not there, and did not experience what they had, so Norman could not judge the tank crew's actions.
Scott215
Gordo brought up the horse thing because him and the other (original) crew members were not happy with Don and Norman enjoying a nice, quiet meal without them. He even say's "You weren't there" meaning Don sharing this with Norman when he hadn't yet been through much war time like all of them had, together. They also say "We weren't invited", "Why weren't we invited." The horse story was to get at Don for not inviting them and sharing it only with Norman.