the speed is actually the number of units it moves at once, it is now 1 unit(integer), and has to be an integer like 2,3,... that 1 unit is the size of each piece of the snake, so if speed is increased, the size of snake's each part has to be changed accordingly (ie: the faster the snake the bigger it's body parts gets).
as I can see here, everyone hates slow snake, so I try to do something.