I didn't use uniq() because I need unique keys, not values, so I'd have to call keys() twice and then use uniq() on the results. I figured this was simpler, LOL. I guess I was just surprised---args are so flexible in Perl I figured that keys() would be able to operator on an overlaid pair. But I guess it's no different than push() requiring the first arg be an array (not a list, not an arrayref, but an actual array).