Character mistake: The bartender in El Dorado was John Mitchum - Robert Mitchum's real life brother. "Elmer" was the character name of the bartender, as mentioned twice in the first saloon shootout mid-way through the movie and in the movie credits under "Elmer, Jason's Bartender." Robert Mitchum mistakenly calls to the bartender, "freeze it right there, Johnny" (inadvertently using his brother's real name, "John, " as opposed to his character's name, "Elmer") in the final saloon shootout scene. (01:20:59 - 02:00:22)
Character mistake: Mississippi is about to go out the door after some men but Cole stops him. A fight ensues and Mississippi shoots the men with his shotgun. Cole then has an attack with his arm because of the bullet in it. Mississippi says, "Cole, what's wrong?" Mississippi knows that he has this problem so it makes no sense for him to ask what's wrong.
Answer: The prime ingredient was Ipecac, a nausea-inducing compound (still used today) which so inflames the stomach lining that it's impossible for the patient to hold anything down. Hot mustard in large doses has a similar effect. The other ingredients (croton oil, cayenne pepper, etc) acted as powerful laxatives, so the entire gastrointestinal tract is evacuated in short order. The gunpowder was a fantasy ingredient, no doubt, as gunpowder is known to cause gangrene of internal tissues.
Charles Austin Miller