There are several Easter Eggs present in The Suffering: Prison Is Hell and it's sequel, The Suffering II: Ties That Bind.
Prison Is Hell Edit
The Gonzo Gun can be found in the level Surfacing. It resembles a chicken that can fire 20 eggs which will kill any malefactor instantly
Secret Room In Chapter 19: And A Child Shall Lead Them you can unlock the entrance to a room in the caves where a dead man representing one of the developers of the game will be found with Dr. Killjoy dancing on his head.
Developer's Commentary After finishing for the first time the game, a new level will unlock. Picking a cowboy hat will reveal a recording of a developer of The Suffering.
Ties That Bind Edit
- Find the Pawn Shop after you leave Torque's apartment.
- After Killjoy opens the backdoor, investigate the bathroom.
- A short cinematic will start and kill the man hiding inside.
- Enter the bathroom:
--- Turn the light OFF,
--- Turn the sink ON,
--- Quickly flush the Toilet 3x,
--- Turn the sink OFF,
--- Turn the light ON.
- Return to the front room.
- In the far corner is a Swizzle Stick propped up against the front wall.
- Destroy it.
- Continue as normal through the Pawn Shop's back door.
- When you reach the room above the canal, a Slayer is suppose to burst through a wall, Captain Carafe will appear instead.
- Wait until he starts to attack.
- Destroy him and he'll drop his Swizzle Stick weapon.
- One hit from the Swizzle Stick will cause your enemy to explode![Source]
Secret Room In chapter 19 a specific series of moves will unlock a room that can be reached from the first area you find in the level. There you will get a phone call. Answer and you will hear the line said by a mysterious voice from the first game. "Dr. Killjoy made the voices in my head go away. Now all I hear it is his voice."