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Here's a pleasantly futile task which should help you while away a few hours when you've got nothing better to do.

Can anyone explain this to me, in a manner that I can understand, please?

Why does this: 

my $var;
my @vars = qw(one two three);
for $var (@vars) {subroutine()};
sub subroutine {print "var is $var\n"};

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Give:
var is
var is
var is
Yet this: 
my $var;
my @vars = qw(one two three);
for (@vars) {$var = $_; subroutine()};
sub subroutine {print "var is $var\n"};

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Gives this:
var is one
var is two
var is three

It's making my head hurt! :-)