1) The guard throws food in to you but you can also pick it up and throw it
back out of the cell. if you keep doing this you will trigger a cut-scene.
During that scene there is an R1 option. If you look on the back of Johnny's
picture you'll see the frequency 144.75 written on the back. Y'know what that
frequency does? It opens the door of the cell. When the game resumes keep
throwing the food out and Johnny will keep eating it, ultimately giving him a
bad case of the runs. When he runs out of the cell area to the bathroom enter
in the radio frequency. When the door unlocks run out of the cell and exit
the torture room through the door at the end of the hallway.
2) A more up-front approach is to simply enter 144.75 into your radio and go
out and attack Johnny. You take some damage by doing this but it is much
faster.
3) Use the Fake Death pill. Haven't used that one much, eh? Johnny will
rush into the cell and see what is going on. When he does, take the Revival
Pill, attack Johnny, and escape.
4) Use the Survival Viewer to spin Snake around. When you exit the viewer
Snake will vomit. When the guard sees this he will rush into the cell to see
what's going on. Knock him out and continue on your merry way.
http://www.gamefaqs.com/console/ps2/game/914828.html