Stupidity: The type of steak that Clyde demands has a sharp kind of bone inside that can easily be used as a weapon. No prison would be foolish enough to overlook this fact, especially as the warden had everything double-checked.
Stupidity: Despite the fact that Clyde is somehow very easily managing to kill people from his cell, it never occurs to assign some kind of security or a camera where he could be consistently watched in case he did something out of the ordinary. Nor did they even both to thoroughly scan his cell, something which should have been done in the first place for any irregularities, and especially once again after it became known that he may have been still killing people despite being locked up.
Stupidity: The first time they go into Butler's garage next to the prison they are breaking in, but Butler never witnessed any break in clues to raise his suspicion. They replaced the lock with the exact same lock. It is clear that they didn't know that this was his access point to the prison, but once they found out there is no way to cover up that someone compromised the facility. How is Gerald sure that the bomb will remain under the meeting room while on his way back to the cell? He has a camera in the meeting room but in the bomb room he didn't bother to put one.
Answer: To make sure he was placed in solitary confinement. The warehouse that he owned and operated out of that was next to the prison also had a tunnel connected to every cell in the solitary wing. Clyde needed to be in one of the solitary cells so he could leave the prison whenever he needed to unnoticed, which also served to make it look like he had an accomplice on the outside.
Phaneron ★
When Nick is talking to a spook later in the movie, he is quoted as telling Nick: "That cell-mate that he killed, you think that was random? No. That's a pawn being moved off the board. Anyone who had anything to do with that case, he's gonna be coming after you." Just as all deaths played roles in Clydes game, as the audience we are led to believe this inmate played a role, but were never given any resolution as to what significance it was. Not a big deal in grand scheme of things, but unexplained.
I don't know if you just didn't read the answer thoroughly or if you didn't pay close attention to the movie, but Clyde killing his cellmate was far from being unexplained. He can't leave the prison if he's in a regular cell with the general population, so he kills the cellmate in order to get placed in the solitary wing, because every solitary cell is connected to the tunnel in his warehouse that is next to the prison, which allows him to leave whenever he needs to.
Phaneron ★