Sierra sat there, a thoughtful look on her face, until finally she raised her hand. "Professor, there has to be something else operating the train besides just magic alone. Otherwise, if someone happened to innocently cast Finite, the train would just stop all at once, right?" she asked. It made sense to her. That was the spell that ended all other spells in effect...

Maybe somebody did cast Finite...

"If somebody did this on purpose, though, they must have only wanted to slow us down, not prevent us from getting here at all. They'd have stopped all over access points," she said, working through some thoughts.

Why would they have wanted to slow them down?

...and none of this really had anything to do with what the professor asked, so maybe she should dd a little something else. Ermm... "So I think somebody needed us stalled for something, but...I can't imagine what."