A brain surgeon's central heating went out on a bitterly cold Saturday night.  He rang the local plumber, and asked him to fix it, now,  no matter what the cost, which he knew would not be cheap.

The plumber duly arrived, spent a couple of hours replacing corroded valves and soldering pipe joints and the like, and then  gave the  surgeon his bill.

The surgeon looked at it, went pale, and said, "Yow ... I don't make this much for two hours' work, and I'm a brain surgeon."

And the plumber replied, "Yeah, I didn't make that much either, when I was a brain surgeon."