' Jeopardy ' champion and author Ken Jennings examines those pieces of wisdom we learned from our moms in his new book 'Because I Said So.' Will gum really stay in your stomach for seven years? Is your life really at risk if you swim after eating? Here are 10 of the "mom myths" Jennings examines in his book.

1. Staying away from a window during a thunderstorm Parents always tell children eager to watch storms to stay away from windows while lightning is flashing. Technically, they're right – Jennings says that lightning can go through a window that's closed, and there's often metal on a window, which can electrocute you. However, while it's never a bad thing to be on the safe side, Jennings says there are only about 300 lightning mishaps a year in America. That puts chances of you being hurt by a storm at what is actually one in a million. "There are also costs to never getting to watch a dramatic lightning storm pass by, poetry-of-the-soul costs not easily measured by actuaries or the National Weather Service," Jennings writes.

2. Swimming an hour after you eat Jennings says that if you eat a huge meal and then go immediately into the water, you may feel uncomfortable – but you can just get out of the water. No one's ever been cited as drowning because they cramped up after eating. The American Red Cross doesn't even mention food in its swimming safety rules.

3. Rusty nails are worse to step on If you step on a nail, you are in danger of getting tetanus, but rust is just a chemical that's on the nail – it doesn't make the nail more deadly. Tetanus comes from a spore called clostridium tetani, which can be found everywhere. A rusty nail has just as much, and as little, a chance of giving you tetanus as any other object you step on that pierces your foot.

4. Razors in Halloween candy Parents have been combing Halloween candy for tampered-with items for decades, but Jennings says there has never been a reported case of anyone poisoning Halloween candy and giving it out, ever. Occasionally a child claimed that they had suspicious candy, but it was always a hoax.

5. You lose your body heat through your head Many parents have admonished their child to put on a hat in cold temperatures because they claim that 50 percent of a person's body heat is lost through the head. If everything else was covered and a head was bare, then body heat would escape through that, but Jennings says that this would be the case for any body part that was left uncovered in the cold.

6. Feed a cold, starve a fever Jennings said that this has been proven to be untrue, and that if you're hungry when you're sick, you should eat, regardless of your symptoms. If you're not hungry, you shouldn't force yourself to eat. But a fever doesn't mean a patient should swear off all food.

7. Soda will settle your stomach Staying hydrated if you have the flu is important, but Jennings says soda isn't the best choice and that doctors actually advise against taking soda while suffering from an upset stomach. Because soda has so much sugar, it can actually make your stomach trouble worse.

8. Cracking your knuckles will give you arthritis No connection has been made between people who developed arthritis and those who cracked their knuckles when they were younger. In one extreme example, researcher Donald Unger cracked the knuckles on his left hand at least twice a day as an experiment into the claim and never had arthritis in either hand.

9. Gum doesn't digest for seven years Gum is usually digested over a twenty-four hour period, not seven years. There have been cases of young children who swallowed gum five to seven times per day, and that did lead to digestive problems that required medical attention, but the odd case of accidentally swallowed gum won't hurt anyone.