A slimy ball that randomly appears in your dryer after you leave it on over night, some northern cultures eat it as delicacy. A night ball is mostly made of mucus that is collected in the anal cavities and then transferred to ones under bridges and then the dryer
"Hey kate, can I use your phone as a light so I can find an outlet?"
"No i'm using it"
"DON'T BE SUCH A NIGHTBALL"