They explicitly state that, contrary to their allusive layout and name, they are "NOT a Web search engine." Soungle does not search the Internets, it only searches their "monster" database. Soungle's goals are to keep it simple to use (search, preview and download) and to keep it free. Because it only searches their database, the results are limited.
A description of the sound appears at the bottom of each sound, followed by the frame rate, duration and bit rate. So there you go. If you need fart sounds, this is your site.