I'm self studying German these days and learning grammar too.
In the sentence below, what's the grammatical form of
Is it something like present/past participle usage in English?
whistling as in
Whistling his favorite song, He went along the street)
Sie lachten beide zusammen und beobachteten, wie der Mann wieder glücklich pfeifend den Weg entlang ging.
They both laughed together and watched the man whistling happily back down the path.