A metaphor is said to be mixed when two different images are used at the same time, often giving rise to ludicrously incongruous and indeed impossible pictures in the mind. One frequently quoted example is this, attributed to the Irish politician Boyle Roche (1743â€“1807):
- Mr Speaker, I smell a rat; I see him forming in the air and darkening the sky; but I'll nip him in the bud.
where the speaker apparently tries to give an impressive flourish to his clichÃ© 'smell a rat' by adding detail to the picture, only to confuse it with a conflicting picture of a gathering storm, and ending by using another, contradictory clichÃ© - although DNB says that "Many of his famous 'bulls' covered potentially embarrassing moments for the government by reducing the house to laughter."
Writers should use metaphors - and all images - with thought and care. Although many speakers mix metaphors as casually - though not often as surreally - as Roche, writers have time to think and should NOT mix metaphors, unless deliberately, for example for comic effect.