At first I just decide to use stutter as a noun:
David pulled himself away slowly, his face as pale as a ghost's. Some words came out of his mouth. At first, they were just incomprehensible stutters, but then they gradually began to take shape. "Y-you're...you're not Sophia."
But then for some reason, it started sounding a little strange to me. Is there any other word to use in cases like this?