Plot hole: When Malfoy gets into trouble while trying to catch Harry with Norbert, Professor McGonagall dismisses his claims as "utter rubbish", and a "cock and bull story." To prove his story was true, Malfoy could have shown her the letter Ron received from his brother Charlie (which Malfoy accidentally received when he borrowed a book from Ron), which detailed their plan to deliver Norbert to Romania.
Suggested correction: Malfoy being a spoiled, privileged child who is used to being taken at word; it makes sense that he would be so taken aback by McGonagall not believing him that the thought simply didn't occur to him to show her the letter at the time. That honestly happens to all of us. We were so emotional in the moment that we couldn't think of the best thing to do until after the moment was over and it was too late.
