As John said, it definitely needs more context to make sense, and what you provided was not enough for that, even with the added part. But I found the text with Google. The context needed would be something like: "A writer wrote a letter to Alan Rickman, saying that he was thinking of writing a biography of him, and wrote the line: "I informed....salts". An Elephant Gun is a suggestion that Rickman might want to shoot him for suggesting such a preposterous idea. The smelling salts would be a suggestion that Rickman might want to try to 'bring him around' from his delusional state - i.e. that the writer was dreaming, or deluded, to suggest such a strange thing, and the smelling salts might 'revive' him.

It would depend on context. An elephant gun is a large caliber, powerful gun for killing elephants. Smelling salts are a substance that releases ammonia gas and can cause a person who has lost consciousness to regain consciousness by triggering an inhalation reflex. It's not clear, without more context, why the author is referring to these two (seemingly unrelated) things.