It is generally held that jokes benefit from brevity, containing no more detail than is needed to set the scene for the punchline at the end. In the case of riddle jokes or one-liners the setting is implicitly understood, leaving only the dialogue and punchline to be verbalised. However, subverting these and other common guidelines can also be a source of humor—the shaggy dog story is in a class of its own as an anti-joke; although presenting as a joke, it contains a long drawn-out narrative of time, place and character, rambles through many pointless inclusions and finally fails to deliver a punchline. Jokes are a form of humour, but not all humour is a joke. Some humorous forms which are "not" verbal jokes are: involuntary humour, situational humour, practical jokes, slapstick and anecdotes.