Here's why:
* Prepositional Phrases: These are groups of words that begin with a preposition (like "inside," "in," "on," "under," "with," etc.) and end with a noun or pronoun (the object of the preposition).
* Function: Prepositional phrases can act as adjectives (describing nouns) or adverbs (modifying verbs, adjectives, or other adverbs).
In this case, "inside his trouser pockets" acts as an adverbial phrase, telling us where something is located.
For example:
* He kept his keys inside his trouser pockets. (The phrase modifies the verb "kept" by telling us where he kept his keys.)
* The money was hidden inside his trouser pockets. (The phrase modifies the noun "money" by telling us where it was hidden.)