“Something smells good! My mouth is watering already.”
Your friend is cooking dinner for you. He's starting to cook. The food smells really good, so you say something about it.
Something smells good! My mouth is watering already.
This is a way that people describe smells:
Something smells delicious!
Something smells like garbage! Ew!
When a person sees or smells delicious food, their body starts to prepare to eat. One thing that happens is that your mouth produces more liquid. In English, we say that your mouth is "watering".
You can use the phrase "my mouth is watering" to describe the feeling of being excited to eat something:
Mmm! My mouth is watering!