The inspection of mistakes can play a powerful role in an individual's learning process (Boaler 2015). The purpose of this article is to support the reader in selecting mistakes that can be leveraged to benefit the learning of all students. Specifically, the authors focus on "which" and "why": "which" mistakes to inspect and "why" these mistakes are inspection worthy. The authors introduce types of mistakes along with ideas to consider when deciding whether a mistake is worthy of class inspection. Then they apply these ideas to a scenario taken from one teacher's classroom.