Get all images attached to a wordpress post except for the thumbnail image.

gistfile1.php

function slideshow_hero($postid) {
		$thumb_ID = get_post_thumbnail_id($postid);
		$args = array( 
			'post_type' => 'attachment', 
			'numberposts' => -1, 
			'post_mime_type' => 'image',
			'post_status' => null,
			'exclude' => $thumb_ID,
			'post_parent' => $postid);
		
		$attachments = get_posts($args);

      if ($attachments) {
  			foreach ($attachments as $attachment) {
    			// Do stuff with your iamges
    		}
  		}
}