Cool things to try:
     Go into the room where the guards lockers are. Open up the locker
in the far upper left corner and there will be a poster of an oriental
woman  in  a  black bikini. Press up against the wall and knock on the
poster. You will hear a funny noise when you hit a certain spot on the
poster.

     First  sneak  up behind a guard with your gun drawn (make sure it
is  empty!!!)  he  will then raise his hands signalling he surrenders.
Try  and shoot your gun, but since it is empty it will make a clicking
noise.  The guard will hear this and realize you can hurt him. He will
then shoot you , so be prepared.

Blood masks:
     After  knocking  out a gaurd or killing one equip the usp and aim
for  they're masks. Shoot them sevral times to make the mask fill with
blood.

Blood everywhere:
     After  knocking  out  or  killing a guard equip the usp and shoot
them in their croch sevral times and then there will be blood over the
place. (personaly I knock out both the guards and waste all 61 bullets
on this trick!)

Bye Bye Brains:
     When  scareing  a  guard  and they are up to a window and your in
back  of  them  shoot  them in the back of they're head this will make
blood fly all over the place.

Make a jerk of the guards:
     When  being chased go around a corner and then just put your back
to  the  wall the gaurds will run past you without noticing your there
making  a  jerk out of the gaurds. (sometimes this doesnt work because
its all based on timing)

To Make guards stand in a stare:
     When  you  go  into  the room with the Guard at the bottom of the
stairs,  and  glass  infront of him shoot the glass once, then aim the
next  bullet to the blue ? mark above his head, when it comes up shoot
it  and  he will, be knocked out but standing for the whole game until
you  leave  the  room,  or another gaurd knocks him. I roll on him and
knock him out on the floor.

To get Snakes biceps working:
     When Snake is hniging pull him up and the lower him (L1+R1+2) His
byceps  will  grow, and so will his grip, after 100 octogan will phone
you up to congratulate you.

Better Grip:
     To be able to hang on a ledge longer just do the following:
     While  hanging  on  a  ledge  go into first person mode (R1) then
press  L2  and  R2 to do pull-ups. Just keep doing that a whole bunch,
taking  breaks  when  your grip gauge gets low (by pressing TRIANGLE),
and Snake will be able to hold on to ledges longer.