There are lots of mice, with identical weight but each with different taste, running from cathode (cage) to the sample (cheese). These mice, after a good or bad meal, will run along the trajectory in the cylinder and go out of the exit to the detector (Cat).
Suppose the cheese is large enough to provide for all the running mice. In fact the mice can only consume the surface of it.
The cat then weighs each mouse, of course eat some, and make a graph of Taste(Energy)-Weight increment(counts). This graph contains the information of the sample (cheese) surface.
This is a schematic illustration of a cylindrical mirror electron Auger-spectrometer found in a surface science book for cats, in the chapter about Auger electron spectroscopy (AES).
WARNING: DON'T TRY TO UNDERSTAND AES FROM THIS POST!