Word Origins writes that the term commonly used for a cramp or pulled muscle “…gained widespread use in baseball jargon.” The first known use of the term was in the Boston Globe on July 17, 1886. It said baseball player Joe Quest had used the term to describe pains being suffered by other players. It is possible, although not confirmed, that the term originated when Quest was working as an apprentice in a machine shop.  There was an old horse named Charlie that walked as if his legs were stiff while pulling the delivery loads from the shop. Quest supposedly came up with the term “Charley horse” for anyone experiencing pain in their legs.

The Phrase Finder comes to the rescue once again. The expression means something is a certainty. It is “…a pseudo betting term…a pleasant-sounding alliterative phrase which indicated short odds—dollars are valuable but donuts aren’t. The phrase parallels the earlier English expression ‘a pound to a penny’.” The phrase originated in the mid-19^th century, with the earliest printed example found in an 1876 edition of The Daily Nevada State Journal.

The UK Phrase Dictionary explains that the expression means “From the highest authority.”  Bettors are always eager to hear which horse is likely to win a race and are eager to hear what stable workers and trainers believe. “The notional ‘from the horse’s mouth’ is supposed to indicate one step better than even that inner circle, that is the horse itself.” The Syracuse Herald published a comment in May 1913, “I got a tip yesterday, and if it wasn’t straight from the horse’s mouth it was jolly well the next thing to it.”

The Phrase Finder says the expression refers to, “A direct and effortless solution to a problem.” There was an ancient belief that silver had magical powers. There are records of spears and bullets being made from silver to battle evil enemies. Nineteen century fiction has numerous references to silver bullets being used “…against werewolves, witches, the Devil, and all manner of creatures…” The use of the expression for the current meaning didn’t become popular until the Lone Ranger radio show began describing how the hero “…arrived from nowhere, overcame evil and departed, leaving behind only a silver bullet and echoes of ‘who was that masked man’?”  There was a warning published in 1951 about viewing the atomic bomb as a magic weapon. “This is not a silver bullet which can deliver itself or otherwise work military miracles.”

I had always believed this expression is used to describe the need to proceed carefully in a delicate situation. The Internet doesn’t seem to agree with that. It does have a long history as a song. Wikipedia says it “topped the charts” for ten weeks after Nick Lucas introduced it in the musical “talkie” film Gold Diggers of Broadway in 1929. The tune was used in the first Looney Tunes cartoon short Sinkin’ in the Bathtub in 1930. Numerous other singers have recorded the song, including Tiny Tim in 1968. Some think it has a satanic origin, especially if played backwards. It was played several times in the horror movie Insidious.