Will x Shall: Qual a diferença (com uma história engraçada)

Further to the post on the modal verb "shall", I found the following funny story (unlikely to be true) in the internet that captures the essence in the difference between "will” and “shall”:

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Some years ago a Frenchman came to England on holiday. While swimming off the beach at Bournemouth he got into difficulties and waved frantically for help. However, nobody noticed him, or just thought that he was waving to a friend, and he got more and more desperate. Finally he shouted out “I will drown, I will drown, nobody shall save me!” The people who heard him, who had all been to very good schools and spoke in perfectly grammatical English, were convinced by this that he was committing suicide and allowed him to carry on drowning!

What he should have shouted was “I shall drown, I shall drown, nobody will save me”, which might have saved his life!
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