This reminds me of a technique called "backwards buildup" that I was taught years ago at college. In that case we were memorizing lengthy stories word-for-word for oral recitation, and we found that we had more success when first memorizing the last sentences of a story, and gradually building backwards to the beginning.

That way there wasn't the problem of making a strong start, only to peter out towards the end, having forgetten the rest of the story. Once you were able to get off to a good start, the rest was a breeze.

No idea why rats do it that way, though...