What happened in this situation?

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(Maya raises her hand)
Ms. Teacher: Yes, Maya?
Maya: Someone passed gas.
(Another student, Nylo, begins silently laughing)
(Another student, Lia, notices Nylo laughing)
Lia: it was Nylo.
(the entire class begins laughing, except for Maya)

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Why did Lia think it was Nylo and expose them? And why didn't Maya laugh?