Some defects are easier found than others.   This light post installed down a chimney flue is an example of an easily found defect.
An experienced home inspector can determine what kind of damages to expect from different rodents.This very hazardous situation was caused by a squirrel chewing on live wires in the attic.
This panel box, as you can see, was overheating at the time of the inspection and was found at the far end of a 30ft crawl space only being about 25 inches high for access. 
Mold is a very toxic substance basically found in all houses, however conditions have to be right for the mold to grow and flourish.  This mold growing on a damaged floor joist was found in  another dark and damp crawl space.
This photo illustrates a chimney protruding through a roof with absolutely nothing below it except 2 precariously placed beams to hold it up.