sub perl_mouse {
    my %HoH = %{+shift}; # I know @_ to get the parameter but not this one
}

$saw{lc,} # what is lc,?

grep { $count!=$count{$_} } map { ++$count{$_};$_ } map { keys %{$HoH{$_}} } keys %HoH 

# the result of this line is stored in which variable?