Some myths busted

It takes 7 years to digest gum. While it may prove a bit more difficult to break down than organic food stuffs, chewing gum gets no special treatment from the digestive system. Doctors figure this tale was invented to prevent kids from swallowing the rubbery substance.
The Great Wall of China is the only manmade structure visible e from the space.
There are several variations on this folkloric statement, and they are all quantifiably false. Astronauts can spot the Great Wall from low-Earth orbit, along with plenty of other things like the Giza pyramids and even airport runways. But they can't see the Wall from the Moon.