sub foo {
    my $i;
    for $i (...) {
       ...
       if (...) {
          my $i;
          $i = something;
          ...
       }
    }
}
[download]

sub foo {
    my $i;
    for $i (...) {
       ...
       if (...) {
          # my $i;
          $i = something;
          ...
       }
    }
}
[download]

You are right. You are absolutely right.

Any code written like that could have unintended bugs but they will learn a valuable lesson in proper variable naming conventions at the same time.