As well as the eggs listed in the above walkthrough for the achievements/trophies, in the Xbox360 version of the title, there are an additional 11 eggs that players can pick up. These enable players to acquire a game completion percentage in excess of 100% on the game's Xbox Live leaderboards. Fortunately, once you have completed the game, you can load up any chapter from the menu and quickly acquire these.
Note: As this particular section of the guide can only be used by those who have purchased the game on the Xbox360, the chapters listed will correlate to the chapter listings in the Xbox360 versions' chapter select menu. As such, they will not correlate to the walkthrough above.
Here is a list of the non-achievement related secret eggs listed in order of appearance in the game and a little guide on how to obtain each of them:
Egg 1: Chapter 8 Location: **** In the area with the mine cart and the rope suspended above the two spiked cogs. Climb the rope here and once the rope stops coming down, jump back to the ladder on the left. Climb up and run to the left into the previous chapter. Drop down into the first hole you come across for the egg. Quickly jump out again unless you want to be impaled by spikes!
Egg 2: Chapter 9 Location: Load up chapter 9, from the start point immediately run to the left.
Grab the crate and push it as far as you can to the left and position it so it is sitting on the edge of the ledge. Return to the right, scare the creature into the hamster wheel and get the rain to start. Once this has been done, run back to the crate, there should be an egg on top of it.
Eggs 3-5: Chapter 14 Location: **** From the location of the above egg (for the achievement Alone in the Dark), run to the right until you hit a wall. Hold the action button and hold back on the stick, you will pull out a block. Jump onto this and onwards. Continue to the right to find egg 8.
Just after egg 8, listen to your characters footsteps. If you listen carefully, you will hear him stand on something that sounds a little different. Continue to the right until you hit another wall. Jump up here, then turn around and perform a running jump to the left, he should land on the strange sounding ground and fall through to an area below. Follow the passageway down to the right to find egg 9.
From here continue right until you hit a wall again, this time press down on the control stick and drop down to a platform below. Run to the right and jump up when you reach a wall. Continue to the right and you will see egg 10 below you. Listen for your footsteps, when you hear clanging drop off the platform to the right and hit the use button, pull the box out of the way, and then jump down to grab the egg.
Egg 6: Chapter 17 Location: After starting the room rotating for the first time and you climb the first cog, continue to climb it and head all the way over the top of it and to the right. In the darkness above the cog you will find the egg.
Egg 7: Chapter 21 Location: **** Load up chapter 21 and drop down into the pit. Grab the box furthest to the right and push it over and activate the gravity switch. When the timer expires, quickly drag this same box to the right wall, so that when the other box returns, they have changed places. Push the box that is now furthest to the right past the switch and up the hill. Let the box go and run and jump onto the second box to reach the starting platform. Once the gravity switch has been activated and the time expires, grab the box as it is sliding down the ramp.
Look at it closely and make sure the top of the box has a couple of small protrusions on it (if not, repeat the previous step until the two protrusions are facing upwards). Push the box all the way back to the previous chapter and push it beneath the vertical gun turret. It should blow a hole in the top of the box. Push the box all the way back to where you found it and an egg will fall out of it.
Egg 8: Chapter 21 Location: **** When you reach the room with the lift and the pair of gravity switches, liberate the two boxes and invert gravity so they are both in the same area. Put gravity back to normal and bring the two boxes to the elevator.
Push one box to the ground level to the left of the elevator, and the second box into the elevator. From here, if your timing is ok, you can push the elevator box on top of the other to have a double stack. Bring the elevator down to ground level and slowly and carefully load them onto it. Hit the switch and ascend with them. Slowly push the box to the right hand wall of the room and climb the ladder. Hit the gravity switch to bring the double stack to the roof next to you. Push the double stack slowly to the left as far as you can go. Then use them to jump up to a higher platform on the left. Follow this to the end for an egg.
Egg 9: Chapter 23 Location: **** Load up chapter 23, run to the top of the vertical wall and jump to the gravity switch and land on the H when it is safe to do so. Wait for the saw to go back down again, and then jump across from the H to the top of the vertical wall. Wait until you can barely hear the saw at all anymore, and then perform a running jump to the left, as you fall hit the gravity panel to be tossed back to the vertical wall. Return to the top and jump to the H again, this time jump off to the platform to the right of the H and you will see an egg fall down from a pipe.
Egg 10: Chapter 23 Location: **** Load up chapter 12. Jump across the neon H to the letter O. You should see a line running through the centre of it. At the end of this line is a handle. We cannot use this yet, but we can position it to where we are able to use it later in the game. Rotate the O by walking slowly near its edges until the handle is pointing about 2/3 of the way down the right hand side of the O. Now play through the game until chapter 23. After getting past the H here, ride the rope down to the O, if you placed it correctly earlier, the handle should be within reaching distance of the solid platform to the right. Pull the handle and the egg will pop out!
Egg 11: Chapter 24 Location: **** This egg appears after the short cinematic following the final puzzle. It will only appear if you have started a new game, played through the entire game in one sitting and have not died once. When you regain consciousness after the final puzzle, run all the way to the left, and then run back to the right, you should see the egg fall from a tree.