A red envelope containing a shrieking, angry message that's impossible to ignore
Harry darted forwards to pick up the letter but Aunt Petunia beat him to it. ‘You can open it if you like,’ said Harry, ‘but I’ll hear...
Harry Potter and the Order of the Phoenix
By J.K. Rowling
‘I’ve been putting out fires all week. People keep sending Howlers and of course, if you don’t open a Howler straight away, it explodes.’