I've never played snake and I didn't understand its movement from the description. One possible interpretation is:

In a snake with head 0, followed by 1, 2, 3, 4, movement is:

tail section 4 moves to the space occupied by tail section 3

tail section 3 moves to the space occupied by tail section 2

tail section 2 moves to the space occupied by tail section 1

tail section 1 moves to the space occupied by head (0)

head (0) moves in the direction specified (either L, F, or R)

Is my interpretation correct? If not, how does snake movement work?