HMmmmMmMmmM...?

"Alright, alright, I get it," he said. “Still, is it something so serious she won’t let your most faithful companion take a look?”

“I have no idea,” Twilight admitted. “It sounded like Luna preferred to speak face-to-face about whatever important business she has with me rather than writing a whole book about it on paper. And that would’ve given you even less chance of reading it to me.”

“You’re really assuming all of this from a short letter?” Spike raised an eyebrow.

“How would you know how long the letter is?” Twilight mimicked Spike’s expression as they walked side by side.

“Because it only took you ten seconds to read it,” Spike replied plainly. 

“Fine,” Twilight said, using her magic to open the library doors. “It is a short letter. Which means if I want to find out what Princess Luna is talking about, I need to leave soon.”