The best paraphrase that demonstrates an understanding of the passage is:
"After catching a crab in the boat, Alice looks carefully over the side into the dark water."
This paraphrase captures key events from the passage, including Alice's experience in the boat, her desire to see the crab, and her cautious behavior while looking into the water. It reflects the main actions and emotions of the characters, indicating that the reader has grasped the context and content of the original text.