The inside track on the Usain sensation
Ever since Sunday night, there's only one thing anyone in Berlin has been talking about: Usain Bolt.
Of course, when it comes to talking sprinting genius, some conversationalists are more interesting than others - which is why I made a beeline for four-time Olympic gold medallist and eight-time world champion Michael Johnson.
Here are his considered thoughts.
ON WHAT HE THOUGHT BOLT MIGHT DO IN THE 100M FINAL
"I actually didn't know what he would run. You take what you know he is capable of doing and then what he's done so far this year, but it's still hard to say.
"You look at some athletes and you know that a big final and being excited is worth something, but for him you don't know what motivates him. He always seems to be so relaxed, so you don't know if adrenaline really flows for him when he starts to run. He's a different type of athlete."
ON WHAT HE DID DO
"It was the most amazing thing I've ever seen. It's different from his 9.69 seconds last year because he shut down 30m from the finish and still ran a world record, but I've never seen a performance like it before.
"I don't think there are very many words to describe the race. It was simply amazing."
ON HOW BOLT DOES IT
"He's 6ft 5in. Traditionally, for an athlete of that height, it's very hard for them to get out of the blocks quickly. He doesn't get out of the blocks quickly compared to the other athletes, but conventional logic would suggest that he would be far, far behind coming out of the blocks. Yet he's able to get out with the other athletes. Relative to the result of the field, he's average coming out of the blocks, which is amazing in itself.
"Once he gets out of his blocks and out of his drive phase and upright, he takes 40 steps for the entire race, where most of the others are taking in the mid-40s.
"He has such a massive stride, he's able to cover so much ground, and his cadence is the same as the stockier guys - take that entire combination and you have something unbeatable.
"That's why at 20m he's right there with everyone else and then he starts to just separate from the field, because he gets so much more out of each step than they do. It's basic maths. The key is that he is able to cover so much more ground so much more quickly than the other runners."
ON HOW FAST BOLT COULD GO OVER 100m
"I wouldn't know where to start to say what he's capable of doing. I wouldn't even know where to begin.
"Where do you start? Do you say he's run 9.58 at such a young age, that he could run 9.4 - who knows?
"The only way to make these kind of predictions is to look at what the bar was for an athlete like him in the past, but there has been no athlete like him in the past.
"His peak? It's difficult to say where he's going to go from here and what's going to motivate him, if he's going to burn out, what his focus is going to be, what his injuries might be like, but at the moment, he has no limits."
ON WHETHER BOLT'S PERFORMANCES WILL DRAG OTHER SPRINTERS TO FASTER TIMES
"I would ordinarily say that's what always happens when someone goes out and sets a mark, but there are two things to consider here.
"Sometimes there's a little bit of a lag - for example in the 200m when I ran 19.3, it was several years until athletes started running 19.5 and 19.6. That could happen in this case.
"And what happens a lot of the time is that the record is put so far out there that athletes start to see it as an anomaly - 'yeah, but that was Michael', or 'yeah, but that was Usain - he's different.'
"That'll be the most interesting thing moving forward from here - what will the other athletes do, how will they find their motivation and how do they solve that themselves."
WHAT WILL HE DO IN THE 200m FINAL IN BERLIN?
"People can start throwing numbers out there if they want, but they're just pulling those numbers out of anywhere.
"You can't predict what he's going to do, because there is no model to go from. You can't say, 'this person did this' - for him, there is no-one like him, there never has been anyone like him."
IS HE THE GREATEST EVER?
"He has to be the greatest ever at this point because he is Olympic champion, world champion and he's shown that he's able to do it again.
"There's nothing to suggest that he won't continue to amaze. If he had gone to Beijing and we never saw anything like that again, it would act as a disclaimer - a great performance at the Olympics but unable to replicate it ever again - but he's shown now that he can repeat and he's here to stay.
"In this era there has been no-one else who has made an impact like him. And, going into the future, his potential influence on sport is even greater than what we've seen so far."