Deep into the Yoyo area, which is the southeast section of Animal Well, you will encounter moving blocks with a small mouse head on them. These moving blocks can have their direction switched, which is necessary for reaching the boss of that area. To switch the directions you will need to use the Yoyo on two different mice in the area.

Elevator Direction Mouse Locations

There are two mice on treadmills controlling the blocks in the area. One of them controls the vertical moving blocks, while the other controls the horizontal moving blocks.

The vertical mouse can be found where the player icon is in the above image.

The horizontal mouse is a bit deeper into the area.

The horizontal mouse is found where the player icon is in the above image. To get the mice to switch directions, just dangle the Yoyo in on the opposite they are currently facing. This will cause them to turn around and run the other way, reversing the direction of the blocks.