Radical
Flock Of Birds

Mnemonic

You open your mouth beneath a tall tree and let out a loud whistle. Instantly, a flock of birds explodes from the branches above, darkening the sky. Your mouth snaps shut in awe as the flock of birds spirals around the tree like a living tornado.
Additional thoughts
Picture yourself standing under a huge tree, whistling upward. The mouth produces the sound, the tree holds the birds, and together they release the flock. Mouth + Tree = noisy roosting spot = Flock Of Birds.
Quick recall
A mouth whistles under a tree, launching a flock of birds into the sky.