Here is the original item:
Because he had eaten a stack of twelve
pancakes,
(A) Emanuel
heard his stomach begin to rumble
(B) as it
processed the food. (C)
Gurgling loudly to protest the huge meal.
You wanted to do this:
Because he had eaten a stack of twelve pancakes,
Emanuel heard his stomach begin to rumble. As
it processed the food. Gurgling loudly to protest the huge meal.
Adding a period after rumble will make As it processed the food a fragment.
You might want to review the rules.