Recently, I've been watching 'Born Survivor' on Channel 4 (a renamed version of 'Man vs Wild' from the Discovery Channel), featuring the superb Bear Grylls. This Saturday he was dropped onto a Polynesian island, where he demonstrated, with aplomb, the techniques for surviving in such an environment, and then constructed a raft from bamboo stalks and banana-twine, with which to make his escape.
There was one thing in particular which fascinated me: trying to retrieve a plastic bottle from the white-water amongst the shoulders of the island, Grylls claimed that waves come in sets of seven, with each wave in a set slightly stronger than its predecessor. Grylls used this rule to count the waves, and then time his excursion to retrieve the bottle. Is this true? I've never heard this before, but it's the type of thing I'd have thought that kids would be told for matters of safety, if nothing else. And if it is true, why is it true?