my $variable = 7;
print $varaible;        # typo
                        # error from strict 'vars'

my $hash = { name => 'value' };
my $key = 'name';
print $key->{'name'}    # derefenced wrong variable
                        # error from strict 'refs'

sub subroutine {
}
print subrotine;        # typo
                        # errors from strict 'subs'