Harry Potter and the Improbable Use of Chaos Theory

The Whomping Willow ominously rattled its branches when they approached.
Granny gave it a cold look and said, loudly, "Gytha? Do you think you could conjure me up an axe?"
There was a pause, an almost considering silence, and then the lower branches were lifted in what could have been considered a hasty fashion for them to walk underneath.