In the kisser!
Recently I went to my new dentist in Oakland. While going to the dentist is rarely much fun, everyone at this office is friendly and professional, and you get good dental advice with very little guilt-tripping. They are also amenable to my treatment preferences, such as getting X-rays every two years instead of every year.
My dentist pointed out two small cavities while I was there. She showed me the cavities with a small mirror, and also had me listen to the sound of metal pick touching my teeth. “Clanking” is good, indicating the enamel is hard. When the instruments sticks and doesn’t clank around, that can indicate the enamel is soft.