"A lot you know," he mumbled under his breath, but replied more clearly.

Locke thought for a moment and mumbled under his breath.

He paused, looked down again, then mumbled something else under his breath.

Then the woman mumbled something else under her breath that no one, including myself, understood.

Some mumble the words under their breath; others sing them out.

He mumbled something angrily at me under his breath and left.

"A lot of good that did me last year," Gabriel mumbled under his breath.

"Don't I ever," she mumbled under her breath before speaking up.

Jack mumbled something under his breath and pushed from the table.

"Perhaps we two are not so different," he mumbled under his breath.