(verb)
to speak in a quick and often unclear manner, as if spitting one's words, usually as a response to confusion or a strong emotion like embarrassment or anger;
e.g. She started to splutter that she hadn't expected to see him home so soon.
(noun)
an explosive choking or spitting sound, for example the sound one makes when speaking quickly or expressing confusion;
e.g. The machine gave a splutter and then shut off.