[RickJWagner]

There’s also a ‘trigger trombone’ variant, where pulling a trigger routes the air through more tubing, bringing a different pitch.

Source: I’m a sponsor of the trombone arts. My kid played trombone in high school.

[acheron]

More formally that's an "F attachment", lowering the key of the instrument (assuming a standard tenor trombone) from B♭ to F. https://en.wikipedia.org/wiki/Trombone#Valve_attachments

See also https://en.wikipedia.org/wiki/Brass_instrument#Trigger_or_th...