The change in point of view in chapter 16 (indicated by parenthesis) helps the reader understand

The mounting suspicions each person has for another

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What Sam Westing was warning of

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Incorrect answer:

The explanation of the clues

Who the suspect really is

The answer is "The mounting suspicions each person has for another." The change in point of view, indicated by the use of parenthesis, provides insight into the thoughts and suspicions of different characters, allowing the reader to understand the increasing distrust and suspicions among the characters.