Marc knew they needed to test the areas that had changed, but as importantly, they needed to test that defects had not been unwittingly introduced as a result. Marc likened the process to an airport luggage carousel, where every difference found in a regression test is automatically captured and tracked in the same way that all the baggage from an aircraft arrives on the carousel. Business analysts (just like passengers) would ‘collect’ the differences they expected and anything still on the carousel would be an unexpected change needing investigation