Hecate stood in what could only be described as a silver and green wet suit. Beside her was a large jar of slimey green stuff. She had her arms folded before her and waited for her Slytherin students to come over. She had her wand in her hand and she pointed it at her throat, silently casting the sonorus charm on it.

Attention All Slytherin Students

Please come to the common room for a meeting with the Head of House.

Then she flicked her wand and conjured a note that said the same thing for the notice board.