Explanation:

- The sentence describes someone having a "sardonic" smile.

- "Sardonic" generally means being scornful or cynically mocking. It often implies a biting humor.

- Let's review the options:

1. Mocking: This means making fun of or ridicule, which aligns closely with "sardonic."

2. Respectful: Showing admiration or high regard. This is the opposite of sardonic.

3. Reverential: Deeply respectful. Again, contrary to sardonic.

4. Deferential: Showing humble submission or respect, which doesn't align with the meaning of sardonic.

- Mocking is indeed the word that best matches "sardonic."

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