Funny Difficult Riddles

Jenn picked a book off the highest shelf in her room. On the spine she read How to Jog. She ran out of the room and opened the book but found it had absolutely nothing to do with jogging.
Explain.......

Answer - The book Jenn picked up was one of a set of encyclopedias; she picked up the volume containing entries beginning with the letters "HOW" through the letters "JOG".