tedster - 6:28 pm on Jan 11, 2011 (gmt 0)
The "%20" is an encoding for the space character. If "/show/" is a form input of some kind on your website, then googlebot may be testing that form to see if it lets them find deep or hidden content on your site.
If you don't have a /show/ directory, then returning a 404 is the right thing to do. This should not cause you any ranking problems, as long as you are not linking to those URLs yourself,either internally or in a sitemap.