The phrase "leave open-mouthed" means to shock or surprise someone to the point where their mouth falls open in amazement. Antonyms for this phrase include words like predictable, ordinary, unremarkable, and mundane. These words suggest that something is not noteworthy or impressive in any way, and therefore will not elicit a reaction of surprise or shock. Other possible antonyms to "leave open-mouthed" include expressions like dull, unexciting, and humdrum, all of which imply that something is lacking in excitement or surprise. Overall, antonyms for "leave open-mouthed" describe things that are less than remarkable, unimpressive, and uneventful.