In the Daily Mail we read of a "sharkman", Mike Rutzen, who tickles Great White sharks to induce a trance-like state.
To successfully swim with sharks, Mike has learned to mimic their body language, changing his posture in response to their actions.
He is seen neither as prey nor predator and the sharks happily glide past him, occasionally letting him ride with them by hanging on to their dorsal fins.
It has not always been plain sailing, though - his body bears more than 30 scars from close encounters. But now he has decided to take on the ultimate challenge - as depicted in this picture - the remarkable phenomenon of "tonic immobility".
This is a natural state of paralysis, which animals sometimes enter when faced with an imminent threat.
However, it can be induced in sharks by turning them on their heads and massaging their snouts, close to the eyes.
The effects last for around 15 minutes and has proved a useful tool for scientists wanting to study shark behaviour. Being able to get so close to the Great White, Mike discovered that they do not have beady black eyes, as previously thought, but they are actually a startling blue.
That's all very well . . . when the shark's swimming lazily around and feeling good about life, the universe and everything.
However, when it's hungry and in a feeding frenzy, I suspect it might not be so easy. I've seen them going for seals in False Bay, South Africa. It's quite a sight.
I mean, how would you like to try to tickle a Great White shark when it's doing this?
I thought not . . .
Full marks to Mr. Rutzen, though, for his courage - and a fascinating story. I hope he doesn't "rub the shark up the wrong way" and suffer for it!