Uh-oh is the little two-part sound English speakers make the moment they realise something has gone wrong, or is about to. It is said with a small catch in the middle — 'UH-oh' — high then low, and that shape is doing most of the work; the meaning is really in the tune. You use it when you spot your own mistake ('Uh-oh, I sent that to the wrong person'), when you see trouble coming ('Uh-oh, here comes the boss'), or when something small goes wrong in front of you, like a glass wobbling. The feeling is mild. It fits spilled milk, a forgotten form, a car that will not start; it does not fit real disaster, and using it for one sounds cold or joking. It is warm and very informal — parents say it to babies all day long, so it carries a slightly childlike, gentle flavour, and it often softens a mistake rather than making a fuss about it. In writing you will see it with the hyphen, uh-oh, mostly in dialogue, messages and comics. It stands alone as a whole turn, or sits at the front of a sentence.