You begin the adventure in a cell.
Zoom in on the bottom right corner on the bones.
Take the eye from the skull.
Take the bone from the left side.
Exit the rat area.
Use the bone on the mushroom on the floor, just left of the door.
Combine the bone-with-sticky-stuff with the eyeball.
Go back to the rat room.
Click on the rat... he will tell you to play this notes... then he plays the 5 notes of "La Cucaratcha".
If you number the bones from 1 to 7 (left to right), then play:
Now play the second part.
Now take the key... that turns out to be a scissors.
Use the scissors on the strange wall on the left.
Well done on solving the Ballad of Ketinetto Part 1.
Hope you enjoyed my walkthrough solution.