Learn Polish: Przyniesiono szczekającego psa do gabinetu. - A barking dog was brought to the consultation room.

It is built from the verb szczekać (to bark). You take the third-person plural present tense form szczekają (they bark), drop the -ą, and add the suffix -ący to get the base adjective szczekający (barking). Since it modifies the direct object psa (a masculine animate noun in the accusative case), it declines exactly like a normal adjective, taking the -ego ending.

Why does the verb przyniesiono end in -no?

This is the impersonal past tense form of przynieść (to bring). Polish uses special verb forms ending in -no or -to to talk about a completed action in the past where the subject is unknown or unimportant. While it translates naturally to the English passive voice (was brought), grammatically it works more like saying "someone brought".

If the dog is the subject of the English sentence (A dog was brought), why is pies in the accusative case (psa)?

Because the Polish sentence uses the impersonal verb przyniesiono, it functions grammatically as an active sentence with an unspecified subject (Someone brought a barking dog). The dog is the direct object receiving the action, so pies and its matching participle must both take the accusative case.

Why does the word gabinet change to gabinetu?