Four doctors who hadn’t seen each other since their surgical residencies met at a medical seminar. Adjourning for dinner and drinks, they turned their conversation to, who makes the best surgical patients:  

The first said, for sure, electrical engineers. “You open ‘em up,” he contended, “and everything is colour-coded.”  

“Nah,” said the second. “It’s librarians. You open them up and everything is in alphabetical order.”  

The third scoffed. “Of course not,” he said. “It’s accountants. You open them up and everything is numbered.”  

“Safety Managers,” said the fourth, with a shake of his head. “It’s Safety Managers, you idiots! No heart, no guts, no spine, and the ass and the brain are interchangeable.”