I was 23, under-prepared and nervous. So when I entered my examiner’s cramped office, piles of papers and books all over the floor, I knew that the viva wouldn’t go well. The experiments I’d done in the first year of my Ph.D. had yielded conclusive results, and I knew that my report was well-written, but everyone knew that the Scottish Professor was mischievous. He was notorious for asking the killer question at the end of a guest lecture, causing the visiting academic to bluff and bluster, digress and divert, the audience secretly pleased by this pricking of pomposity; and yet now it was I who was about to be found lacking. Worse still, the killer question came at the start of the viva rather than at the end.

"Can you explain what E.S.R. means?"

I gulped. This appeared to be a straightforward question, so why were his eyes twinkling?

“E.S.R. stands for electron spin resonance. I’ve been using E.S.R. spectroscopy to detect sulphur-containing radicals. My supervisor and I found some errors in a paper that was published a while ago. It came from your lab…"

"Yes," he said curtly, "but why E.S.R.? Why not E.P.R.?”

My mind emptied.

“Well, um… E.P.R. stands for electron paramagnetic resonance. The unpaired electron on the radical displays spin as well as… paramagnetism? So, um…” What the hell was he getting at? “Either term is okay.”

“No!” he exclaimed gleefully. “All electrons display spin. Yet it is only unpaired electrons, radicals, that display paramagnetism. You shouldn’t have used E.S.R. throughout your report. It lacks precision. You’ll have to change it. Anyway…” he waved his hand, dismissing my idiocy. “On to these experiments then.”

I looked down at my feet and sighed. This was going to be a long afternoon.