How does Beatty discover Montag’s green bullet?

Beatty discovers the green bullet when he hits Montag in the head and it falls out of his ear and onto the ground.

Beatty struck him a blow on the head that sent him reeling back. The green bullet in which Faber's voice whispered and cried, fell to the sidewalk. Beatty snatched it up, grinning. He held it half in, half out of his ear.