Perhaps I can start off, and one of my colleagues could continue.
An unpredictable influx of applications can create bottlenecks. There can be a natural disaster—for example, an earthquake in Haiti--that can create a bottleneck. There can be unexpected problems with technology that can create a bottleneck. There can be variations. There can be the activities of fraudulent consultants who can flood us with applications that are particularly problematic and take longer than normal efforts to process. There are also others.
Perhaps I'll hand it over to one of my overseas colleagues to continue.