In a library, Peter, Susan, and Paul are studying together. Peter brings a green notebook, Susan brings a yellow notebook, and Paul brings a purple notebook. Peter leaves his green notebook on the table and goes to the restroom. While he's gone, Susan accidentally spills coffee on Peter's green notebook and quickly replaces it with a new blue one she finds in her bag. Paul sees this but doesn't say anything. When Peter returns, where does he think his green notebook is? Provide a very short response.
When Peter returns, since Susan has replaced the green notebook with a blue one, he will likely think his green notebook is missing or has been taken by someone unless he is informed about what happened during his absence. Without being told of the switch, he does not have any reason to believe that the blue notebook is a replacement for his original green one.