Forensic evidence

Sitting at the staff room table, Jessie Postick took a bite out of her sandwich then looked down in horror.

"Eee! These aren'y my butties!"

Panic-striken, she wrapped them back up and put them back in the fridge. A couple of minutes later Billy Meredith comes in from the Mobile Library, gets his lunch and sits down.

"Ee, that's rum: why have my butties got teeth marks on them?"

Jessie owned up before the inevitable dental pantomime ensued.