Nedarim 21: If It Walks Like a Duck, and Quacks Like a Duck, It's Still Not Always a Duck
Chapter 3! The opening mishnah addresses nedarim that are not real vows, but look and feel like a neder, and therefore should not be said. Exaggerations or circumstances beyond one's control, among others. Plus R. Tarfon on unclear, conditional formulations. Also, how and why those who utter these not-vow vows need to see a Torah scholar in order to get out of them. Plus, the stories of those who needed that kind of consultation exactly.