1): Aha - it's a fallback. Full code from File::Find:

# check whether or not a scalar variable is tainted
# (code straight from the Camel, 3rd ed., page 561)
sub is_tainted_pp {
    my $arg = shift;
    my $nada = substr( $arg, 0, 0 );    # zero-length
    local $@;
    eval { eval "# $nada" };
    return length($@) != 0;
}

# We need a function that checks if a scalar is tainted. 
# Either use the # Scalar::Util module's tainted() function 
# or our (slower) pure Perl
# fallback is_tainted_pp()
{
    local $@;
    eval { require Scalar::Util };
    *is_tainted = $@ ? \&is_tainted_pp : \&Scalar::Util::tainted;
}
[download]

And i'm banging my head against a wall to understand it. This code mucked my day ;-)

Best regards, Karl