Clone out toy mouse from cat source.
Cut out and add mouse from mouse source and warp tail to fit in bottle.
Adjust colors of mouse to match the cat.
Add mouse shadow.
Cut out bottle. Cut lid off bottle.
Place mouse inside bottle and make bottle transparent.
Select the bottle area and slightly blur that area of the cat layer. Also warp the tongue and paws a bit to make it look like the bottle is causing a slight distortion effect.
Add forward shadows to bottle to look like the same forward shadows on the cat.
Select the wall behind the cat and paint over it.
Copy the painted area and render clouds.
Slightly blur the rendered cloud layer to cover the source background.