Why are bananas curved?

The new book, Do Cats Have Belly Buttons, answers useless trivia questions like:

Why are bananas curved?
Bananas grow on tall trees in big bunches around the top of the trunk. Their curving shows how efficient nature is. Their shape means they can fit very closely together, which allows more bananas to grow around the tree - as many as 50 in a bunch.

Why does a drink fizz up when you drop an ice cube in?
In a liquid, gas bubbles are formed when they attach to a solid surface. They form especially well when placed against something rough. So, in a liquid drink there are thousands of tiny potential bubbles in the dissolved carbon dioxide jostling for position against the wall of the glass, hoping to take shape. When a rough ice cube is placed in the drink, the carbon dioxide fights to attach itself to the cube so it can shape itself as lots of gassy bubbles. It prefers the ice cube to the glass because of the roughness of the cube.

What causes the feeling of butterflies in the stomach?
These are actually small muscle contractions in the digestive tract. The gut's muscles are normally well co-ordinated - but when disrupted by stress, the body's priority is no longer digestion. So, rather than wasting vital blood and oxygen supplies on processing food, the body diverts them to the legs where they can be better used - for example, to help us run out of the way of danger. The gut is therefore shut down by the brain, leaving it with irregular rhythmic contractions.

Can chewing gum get tangled up in your intestine?
Many parents have warned their children this might happen - but it simply isn't true. Although gum can stick to shoes, bus seats, hair and pavements, it makes its way unhindered through the digestive system - passing straight through the stomach and on to the intestines. It cannot adhere to the moist and slippery walls of the gut.

[from Daily Mail via Reddit.com]