What's at the bottom of the ocean? Who put an 's' in "lisp"? Why is there only one word for "thesaurus"?Life is filled with endless mysteries, although, admittedly, some are more interesting than others. From the disappearance of Amelia Earhart to the building of Stonehenge and the numerous theories that indicate that ancient civilizations had contact with South America long before Christopher Columbus, these many mysteries have led to countless questions and innumerable hours of head scratching.From science to the arts, from history to modern technology, there are mysteries everywhere you look. On the following pages, we look into some of these mysteries that have had scientists and experts wracking their brains for decades if not centuries but to no avail.Take these perfectly spherical, 600-year-old stone balls found across Costa Rica: How did they get there? Who made them? And what do they mean? These are just the tip of the iceberg.