This is because when using print or say, there is ambiguity in what you're passing. Without the parens:

perl -w -E 'say (localtime)[1]'
say (...) interpreted as function at -e line 1.
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say like print are both functions. perl just makes it convenient that you can omit a function's parens in most situations. say believes that the opening parens belongs to itself, like this: say( localtime )[1] ;, which is wrong. So if you look at it like this: say( (localtime)[1] );, it may become clearer as to what's happening. In most other cases, you can eliminate the parens:

my $x = (localtime)[1];
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or

return (localtime)[1];
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