Some nouns change
My mom works with many women.
Singular: woman
Most adults have 32 teeth.
Singular: tooth.
We saw many geese at the park last week.
Singular: goose
Other nouns have the same singular and plural form.
Some people say counting sheep can help you sleep at night.
We saw many deer during our visit to the forest.
My uncle and his friends caught five trout on their fishing trip.