Oho is a small cry of noticing. You say it when something suddenly becomes clear, or when you catch someone out, a bit like aha. It can sound pleased, teasing, or as if you have found a secret: “Oho, so that’s what you were doing.” It is not angry, and it is lighter than a shocked oh. It is not “oh no” either — that is worry. It feels rather old and story-like now: you will see it in books and plays more than hear young people say it in the street. For ordinary surprise, people actually say oh or aha.