5. FOXDIE
You can't get much weirder than a virus within Snake's body that kills specific people when he gets close to them. It makes no scientific sense, but apparently, Snake was injected with FOXDIE and was used as a vector by the powers that be in order to wipe specific people off the map. It has something to do with the nanomachine angle, but it's still pretty weird.
4. What Do You Get When You Take "Is" Out of Solid?
You're left with the word "Old", which is the codename Snake uses during his final mission. It's fitting, since he spends the whole game coughing up a lung and groaning about his back.
3. "Time To Switch The Disk..." (MGS4)
As Old Snake retraces his steps through his old stomping grounds at Shadow Moses, Otacon calls him and reminds him to eject the current disk, and replace it with disk 2. "Do you see the disk labeled 'Disk 2'?", Otacon asks Snake. "Uh...no", Snake responds. This was the exact spot in MGS1 when the player actually did have to switch the disk, but MGS1 was coded on a CD, which had a much smaller storage capacity than the Blu-ray technology that MGS4 utilized. "Oh, I forgot! We're on the PS3 system! Blu-ray! Nevermind Snake", Otacon exclaims. "Dammit Otacon, get a grip!", Snake barks. Weird!