Depends on the type of floor over the crawl space now doesn't it.  I've been in several homes where you could see to the crawlspace under the floor.  Yes they were uniformly older homes with wood flooring where the wood didn't perfectly match up.  But then you would have no idea what type house/crawl space he was hiding in either. I've seen some crawl spaces that were closer to 'basements' and others that would take a very very skinny person to get into...