Around early September, 2006, ABC news said that four prison inmates in El Salvador were discovered with mobile phones inside their anal cavities, according to Slate (the original ABC link is no longer working). That prompted Slate to wonder (and answer too) how much stuff a person could handle up the anus. The writing is way too interesting and enlightening to leave it away, though found in a moment of procrastination. Since Slate tends to keep their old articles for quite a bit of months, here's the link. But the answer, for those who don't want to browse there to find out what you can and what you shouldn't stuff up your ass, is this:
In general, it takes a fair bit of training to conceal something that's more than a couple of inches in diameter. As a general rule, the medical literature on "retained colorectal foreign bodies" considers anything bigger a "large object."
For the full fun, of course, go to Slate and read the full article.