inbound - 2:30 pm on Aug 22, 2013 (gmt 0)
If the site is very busy then GA can do sampling of data, so only a percentage of data is processed for some reports, and then uses that to estimate numbers. This can be one reason behind high numbers of wierd searches.
GA used to make it very clear that sampling was happening but recently I've seen it sampling more and more without reporting it.
A way to reduce sampling on busy sites is to get reports that are for shorter timeframes and then stitch them together yourself (we do this with php/mysql but you could use excel if you don't do it often). We have seen considerable differences in the search term figures when taking 30 separate reports for a day each versus a 30 day report.