To send the snake to the point where you want it to go, pull it by the tail and release it after making sure of it thoroughly. In this way, you will be feeding him by fruits and he will move on to the next level by taking the key for you only if you feed him enough! Otherwise, he won't be able to move on the next level since he won't have enough stamina to continue. There are also things that you need to be careful about. Since there are traps on the map, you should try to send the snake to the places far from those traps. So that he will be comfortably fed.