Two hillbillies approach each other on a country road. One is carrying a sack over his shoulder.
 
"Hey, Billy Bob," calls out to the other, "What you got in that sack?"
 
"Some chickens." 
 
"If I guess how many chickens you got, will you give me one of them?"  
 
"Heck, Joe Bob, if you guess how many chickens I got in the sack, I'll give you *both* of them." 
 
"Okay.  Er...  Five?"