# because $_ is an alias, @foo is also modified
my @foo = qw/one two three four five six/;
my @bar = map { s/[aeiou]//g; $_ } @foo;
print join(', ', @foo), $/;

# because we localize $_, @foo is not modified
my @foo = qw/one two three four five six/;
my @bar = map { local $_ = $_; s/[aeiou]//g; $_ } @foo;
print join(', ', @foo), $/;

# not to mention even when you loop through an array
my @foo = qw/one two three four five six/;
s/[aeiou]//g for @foo;
print join(', ', @foo), $/;