A monster lives [in] a cave. (3)

subject = A monster (with three eyes) adjective prepositional phrase
verb = lives
preposition = in
adjective phrase = a very comfortable
noun = cave.

subject = The cave
verb = sits
preposition = on
prepositional noun = top
adjective prepositional phrase = of a mountain Used as adjective to describe the noun ‘top’

subject = The [very friendly] monster adjective phrase
verb = loves
object = animals.

One day,

subject = the animals
verb = come
adverb = over
preposition = for
preposition object = dinner

subject = The monster
verb = cooks
object = a big pot
prepositional phrase as adjective to describe ‘big pot’ = of delicious soup

He uses onions, potatoes, and tomatoes.
He uses fresh onions [from Gansu], sturdy potatoes [from Shandong], and juicy tomatoes [from Xinjiang].

subject = The [very hungry] animals adjective phrase
verb = wait
preposition = for
prepositional object = [the hot, delicious soup] adjective phrase is series of adjectives ‘hot, delicious’ to describe prep obj ‘soup’

subject = Each (deter) animal
verb = gets
object = one bowlful (noun – bowl full amount of food).

subject = They
verb = eat
preposition = until
prepositional object = [their stomachs are full] (prep obj).

The prepositional object

“their stomachs are full” is a noun clause.
An object can take noun clauses.