In the yellow block it says:
URLs (not domain names) are case-sensitive, and so is symfony (even though the method names are case-insensitive in PHP). This means that if you add an executeshow() method, or an executeShow(), and then you call show with the browser, symfony will return a 404 error.
But the second example is actually not an example of a case error - "executeShow()" is the correct method name. I guess this has crept in since, in the original 1.0 version of the book the example was "...This means that if you add an executemyaction() method, or an executeMyaction(), and then you call myAction with the browser, symfony will return a 404 error."
To correct this I would recommend changing the 1.1 documentation to read:
URLs (not domain names) are case-sensitive and so is symfony (even though the method names are case-insensitive in PHP). This means that if you add an executeshow() method and then you call show with the browser symfony will return a 404 error.