Here's why:
* Dangling Modifier: The phrase "After reading the whole book" is a modifier that describes the action of the sentence. However, it's unclear who or what actually did the reading. It seems like the plot itself read the book, which doesn't make sense.
Here's how to fix it:
* Clarify the subject: "After reading the whole book, I thought the plot seemed a little thin."
* Reword to avoid the modifier: "The plot seemed a little thin after I finished reading the whole book."
Let me know if you'd like me to analyze other sentences for dangling modifiers or misspellings!