The familiar rules with the board fenced off. Blocks are scattered across the grid before you start, so the open space is broken up from the first move and the safe loop round the outside that carries most snake players through the early game is simply not available.
Food and block counts sit at the top and both matter. It plays quicker than the plain version because there is less room to be lazy in, and a run that reaches double figures has involved at least one deliberate decision to cut through a gap that was one square wide. Short games, and the failures are your own.