Watch the Help My Onions online guitar lesson by TrueFire from Blues Guitar Greatest Hits - Vol. 4
Help My Onions is a video guitar lesson presented by Matthieu Brandt and is sourced from Chord Tricks For Electric Blues
Many chord tricks only work in certain keys; keys where open strings have an important function, for instance. You can use the open strings as a pedal bass note, play melodies on the top strings, play barre chords without a barre, and color chords up the neck with the open strings. The "Help Me" groove - also used in "Green Onions" - is a great example of this.