Blackmail
"Special delivery!"
Remus looked over his book to see Sirius, holding an envelope in his mouth and looking horrible amused.
"You are drooling on the letter. What is this about?" He snagged the letter from Sirius' teeth and looked at it.
"It is a formal inquisition for your O' so needed presence in the map making tonight."
"Right. So you are breaking rules. Why was the letter in your mouth?"
"Blackmail."
"You are blackmailing me?" Remus raised an eyebrow.
"No-" Sirius grinned widely. "Black-" He pointed to himself. "Mail." He pointed at the envelope.
Remus groaned and dropped his face into his hands as Sirius continued to look and feel very clever.