Four surgeons are discussing who were the best patients to...

Four surgeons are discussing who were the best patients to operate on.
The first surgeon says, 'I like to see Accountants on my operating table because when you open them up, everything inside is numbered.'
The second responds, 'Yeah, but you should try Electricians! Everything inside them is colour-coded.'
The third surgeon says, 'No, I really think Librarians are the best; everything inside them is in alphabetical order.'
But the fourth surgeon shut them all up when he observed, 'You're all wrong. Guess (C) is the easiest to operate on. There's no guts, no heart, no balls, no brains and no spine, and, there are only two moving parts - the mouth and the asshole - and they are interchangeable'.