We just finished a job for a client that had a home they just moved into. They noticed after moving in that their clothes were taking a very long time to dry. In fact, the dryer was getting so hot they could see the element glowing from the back of the dryer. So, they used a lint catcher rather than the vent. Our company was called to clean out the vent along with the rest of the ductwork and their furnace. The picture below is what we found when we cleaned out the dryer vent duct:
This is a bird nest. It was blocking the vent deep inside the wall. It would have been impossible for the homeowner to clean this out without the proper equipment since it was about 10 feet deep into the duct. Not only that, the lint behind the blockage was backed up all the way to the dryer. This was a tremendous fire hazard.