sub mysplit1        { ... }
sub mysplit2 ($$;$) { ... }

my @x = ("a:b:c", -1);
 mysplit1(":", @x);  # arguments to mysplit1 are flattened
 mysplit2(":", @x);  # parsed like mysplit2(":", scalar(@x)) !!!
&mysplit2(":", @x);  # prototype is ignored, arguments are flattened!