What metaphor does Brutus use to describe Cassius's dishonest act?

Brutus uses the metaphor of a "serpent's egg" to describe Cassius's dishonest act. He suggests that, although Cassius may appear harmless at first, his deceitful nature has the potential to grow into something dangerous if not addressed. This metaphor emphasizes the idea that unchecked dishonesty can lead to significant consequences, much like allowing a serpent to hatch and grow unchecked.