At the very start of Chapter 1-1, if you let Chris and Sheva stand idly in the opening spawn area for about 30 seconds after the first chunk of dialogue finishes, a secret conversation can be triggered where Chris talks to Sheva about the impacts of American capitalism.
Defeating Wesker within the 7 minute time frame he gives to the player will earn them the "Heart of Africa" treasure item. It can be found below the staircase leading to the upper level exit.
The drug that was specifically designed to keep Albert's virus in control has this written on the label: "Caution: Don't give to children under 2 years of age except on doctor's advice".
Shinji Mikami, the creator of Resident Evil, didn't play RE5 until 2011, a whole two years after the game's release. This is because he didn't like the idea that someone else had made the game.
At the end of the game, Spoiler:Wesker falls into a volcano and is blown up by a pair of RPG-7 rockets. According to Producer Masachika Kawata, this is really the death of Wesker. "Even if you want Albert Wesker to come back, there is no chance he's coming back from that."
Excella Gionne was originally supposed to be killed by a tyrant, similar to what happened to Albert Wesker in the original game. It would have been Wesker that ordered the tyrant to do so.
Parts of Resident Evil 5's Beta were later used in Resident Evil 6. Mainly, the underground ruins, with parts being under water, Gigante-like giants assaulting a town while you had to protect another character trying to help, and a boss battle fought on a train where you had to run from car to car while fighting it. The monster itself (Irving) was also very similar to Birkin's final form.
While the game was originally not supposed to be a co-op experience, Chris still had a partner to go with him to Africa and Sheva still existed in the game. Chris' original partner was Barry Burton, and Sheva was going to be a part of local militia fighting against the Bio Organic Weapons.