Now I know why our carpets are always covered in filth in this department - we've got the wrong type of carpet.
One of the college cleaners demonstrated how this was possible, attempting to vacuum up a test patch of muck, to prove a point... look, the dirt is still on the carpet, despite the hoover's best efforts to suck it up. That's not because it's a crappy old vacuum cleaner without enough suction power, or the cleaning team's intermittent visits to this department. It's because we've got the wrong type of carpet. Sort of like when you get the wrong type of snow disrupting public transport. Weird logic, but strangely endearing.