Trevor reads a dump over the phone
Most of the folk reading this have never seen a mainframe hex dump. No it has nothing to do with excrement. It is like the huge diagnostic file your PC decides to write in a crisis just when you'd rather it was rebooting so you can get on with work. But when a mainframe produced one back in the 1980s it came out on the old green line-flow paper. Many of you haven't seen that either. A six inch thick stack of continuous fan-folded paper. Miles of it streaming out. Maybe it did have something to do with excrement after all. And when it is a dump, it consists of closely typed columns of number pairs: the hexadecimal memory addresses and their contents.
I worked for a software company. I was onsite trying to fix a client's problem. I rang Trevor at home. Trevor walked on digital water (see other legends about Trevor).
"Trevor the database died again. We're stumped."
"Have you got the dump? Tell me what it says at dog fox able three" [I think they were four digit addresses as I recall??]
"Three two charlie four dog seven able nine" [Likewise I recall eight digit contents]
"OK stick your finger there. Now go back to dog seven able nine, what's it say?"
...and so on. There'd be occasional pauses while Trevor calculated an offset (an address relative to some other address, i.e. a hexadecimal addition or subtraction) or translated an instruction. Sometimes he looked an offset up in a map of them (which went everywhere with him), but not often - he knew many by heart. After ten minutes of back and forth, it dawned on me he had much of the code in his head and he was mentally walking it. "Hmmm we're in the despatcher. That should be pointing to the the top of the Master List but it isn't..." You could make an analogy with playing chess in your head, but it's harder. After ten minutes I also ran out of fingers place-holding in the huge fanfold of paper. This was in the archaic days pre-Post-Its.
I was a little sceptical that he could really do it until the day I was on the other end of the phone, sitting next to Trevor while he did it again. A one-page sketch of the database memory structure, a pencil and notepad, and his head. Awesome.
Made in New Zealand 
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I had a mentor in my early systems programming days similar to trevor. He was an IBMer who spent a lot of time teaching me to read hex dumps .... The backs of blank punch cards were his scratchpad as they fitted into his shirt pocket .... moments of discovery or a result often announced in a loud voice "It's Charlie Alpha Foxtrot" or some other hex reference .... He was qite a guy and retired as an IBM sys prog after working on our account for a couple of years .. A rareity those days in a young profession..... For some the Hex world seemed as natural as the real world .... :O)