Does it sound natural to say "the mouth" when talking about a thing, like for an instrument in this case?
Native speaker’s answer
Rebecca
Yeah! If something resembles a mouth and perhaps forms some kind of entrance or exit, it can be called a "mouth." Such as a container, a river, a bottle, a volcano, a cave, and an instrument like a trumpet or horn. Ex: The river mouth is just ahead of the boat. Ex: Can you wash the mouth of the bottle since you drank from it? Ex: I was so scared when we entered the mouth of the cave.