Which sentence from the paragraph is an example of a smile?

I assume you mean a simile. A simile is a comparison made by using the words like or as: "Her hair was as gold as a lion's mane", "His beard was like tiny wires brushing her skin."

When asking a question, it's good to provide as much information as possible. If you can provide the paragraph in question, I can edit the answer to address your specific question.

The era was mesozoic