The phrase "marched cannon's mouth" is a literary device often used to denote a dangerous or risky endeavor that a person is undertaking. Synonyms for this phrase include "walked a tightrope," "braved the storm," "danced with danger," "played with fire," and "threaded the needle." Each of these phrases evokes a sense of adventure, courage, and excitement. Whether it's crossing a narrow bridge over turbulent waters or taking a risk in business, these synonyms capture the spirit of "marched cannon's mouth." Whatever one may call it, taking risks and living life on the edge can be thrilling and rewarding.