But Carcer was different. He was in two minds, but instead of them being in conflict, they were in competition. He has a demon on both shoulders, urging one another on.

Terry Pratchett, Night Watch; about Carcer Dun

Mad scientists are a dime a dozen. But can you imagine what a mad engineer can do?

It is almost literary pre-programmed that scientists as soon as they become insane start to develop death rays, doomsday bombs, sex-changing viruses or they distorts space-time beyond recognition. All very manageable. Nothing really alarming. Standard stuff, everybody knows it and can adjust to it. Everybody knows it and everybody knows how to deal with it. Mad scientist are nothing to fear.

But can you imagine the horror that a mad engineer can unleash on the population? No? How about giant spider mechas spewing acid and poison? Clothes dissolving mist? And singing "We come in peace. Take us to your leaders!" over wing-mounted machine guns as music.

Self-steering carriages whose operating system goes on strike every time a female sits at the wheel and can only be parked when all the males sit in the back?

And nobody knows how to stop them!

Frighteningly cruel and terrifying. And no one notices a mad engineer until it's too late. Truly diabolical. Engineers don't laugh out loud, mean and gleeful either. They tell jokes about how many people it takes to change a light bulb and then invent a light source that doesn't break. Just twisted devious evil.

A mad scientist loves to play sadistically with his victims. It is deeply frightening that an engineer, in contrast, draws his motivation from making his machines and methods more efficient. A 99 percent kill rate is not good enough. It need to be at least 99.999999 percent.

A mad engineer could be sitting next to you and you wouldn't notice.

Until it's too late.