Almost-right try

[Andrew Schultz]

$b = $a;

$b =~ s/[^newsdu]//i;

if ($b matches) && ($a doesn't) { print out }

Obviously we need to clue misspellings buy may rustle something up here

[Andrew Schultz]

This is still a bit fuzzy, because you may have a problem with whether there is more than one character before. There also may be a problem with slowdown. So I am going to punt on this issue.