A Stock Visual Metaphor trope used widely in animated media. When a character sleeps, sometimes a lot of "Zs" are shown near the character, either in the form of a stream of z's coming from the character's mouth or head, or a group of "Zzzs" contained in a Speech Bubble. This trope used to be shown specifically for people who snore in their sleep. While the sound of snoring cannot be represented easily by letters or onomatopoeia, "Z" was chosen for some reason. The origins of the "Z" may come from the symbol (which looks like a stylized "Z") of the musical note for a full break in tact of the song. The letter eventually became indicative of any sleeping person.