Measurement Scales Question

Question reads:
We trained rats to run a straight-alley maze by providing positive reinforcement with food. On trail 12, a rat lay down and went to sleep halfway through the maze. What does this say about the measurement scale when speed is used as an index of learning?

I honestly don't know how to answer this. I'm a psych major and I already know that speed is a poor index of learning and is probably a better index of motivation. Here's my guess:

If speed is used as an index of learning, I think the measurement scale would have to be ratio. But, given the inherent problems aforementioned, it would be impossible to obtain a score for a rat that went to sleep. They would have to be classified as 'completed' or 'not completed'

Can someone please elaborate or correct my guess,

thanks so much.