Lily jumped, as one did when someone came up behind them, but turned with a smile for the boy. "Merlin, Severus, where did you learn to sneak up like that? Wait. Wait, are you humming?" She smirked, tilting her head to one side to watch him with amusement writ large on her face. "Decided to forsake both morbidity and feistiness and try out the 'cheerful' niche?"