Interesting Dryer Contents

You just never know what you might find in the clothes dryer around here.  A few days ago, the dryer was clanking.  So, I opened the door to see what might be the cause.  It was a couple chunks of plaster that must have ended up in a pocket (?), between clothes in the hamper (?).  I have also found screws and tools,  along with the more run-of-the-mill finds like pens, coins and paper clips.  And I DO check the pockets first!  So what are the mysteries behind finding these miscellaneous items after checking for them, as well as losing only one sock in any given pair?  Anyone?