Putting a hippo's head on a lizard

Today we had a demo where we had to put a hippo head onto a lizard. First we had to re-size the head to be in proportian with the lizard. We then added two adjustment layers, colour balence to make the head green and levels to match the lighness to the lizard. We then went to the hippo layer and using a large soft brush we hid the sharp edges of the head and with a low brush opacity we rubbed enough of the hippo away so the scales underneath were visable. Then we used the quick mask tool to select around the hippo's head then added a brightness/contrast adjustment layer ontop of the lizard layer and made it darker there. Finally we added a new blue layer and set it to overlay and lowered the layer opacity to 30%