The correct punctuation for the given sentence is: "I thought I saw a cat," said Tweety Bird.
To punctuate the given sentence correctly, we need to apply the appropriate capital letters, full stops, and quotation marks. Here's one possible correct version:
"I thought I saw a cat," said Tweety Bird.
In this corrected version, we start the sentence with a capital letter "I" as it is the first word. We also capitalize "Tweety Bird" as it is a proper noun, a name. Additionally, we use inverted commas or quotation marks around the direct speech to indicate that it is being spoken by Tweety Bird. Finally, we end the sentence with a full stop to indicate the completion of the statement.
Remember that there can be multiple correct ways to punctuate a sentence. The key is to use capital letters for the beginning of sentences and proper nouns, and to use appropriate punctuation marks to indicate the structure and meaning of the sentence.