PS2 Pressure sensitive buttons:
L1, L2, R1, R2, X, Square, Triangle, Circle, [D-pad] Up, Down, Left, Right
MGS2 uses Square for aim and fire.. If you hold it loose he doesn’t fire, hard he shoots.
L2, R2 to lean left and right.. Hard he leans more, soft he leans less. L2+R2 together and snake stretch so he can look up over obstacles.