What is the non-animated supposed to have?

There is no way to tell if a gif87a or gif89a is animated by the header.(well maybe deep down in there). Your best bet is to use Image::Info or something similar to check the Image

#!/usr/bin/perl -w
use strict;
use Image::Info qw(image_info);
use Data::Dump;

while (@ARGV) {
    print Data::Dump::dump(image_info(shift)), "\n";
}
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If you run animated gifs thru that you will get a parameter called GIF_Loop, that may be a way of detecting it. Some graphics module may have an is_animated method, but I don't know of one off hand.