beginning sentences again

[Quang Hai]

I am reading a short story. A boy is telling on his dream. but he is too scaring.
"The boy stammered rapidly through his account, beginning sentences again because he realized his meaning had slipped away, speaking more slowly the second time but softening his voice to a pitch that made it almost inaudible."

I do not fully understand underlined words. Please help me to understand the sentence fully. Many thanks!

[bhaisahab]

I am reading a short story. A boy is telling on his dream. but he is too scaring.
"The boy stammered rapidly through his account, beginning sentences again because he realized his meaning had slipped away, speaking more slowly the second time but softening his voice to a pitch that made it almost inaudible."

I do not fully understand underlined words. Please help me to understand the sentence fully. Many thanks!

The boy kept starting his sentences again because he realised he was not getting his meaning across.