An impulsive, seemingly unmotivated action, change of mind, or notion.
A capriccio.
A brief romance.
An unpredictable or sudden condition, change, or series of changes.
A disposition to be impulsive.
Something used to goad or push someone to act.
A stick designed to goad cows, steers, and similar animals in order to prompt them to move in a desired direction, now usually electrified to administer a stimulating shock to the animal.
To goad or push someone to act.