Just scrape the mold off, right? Wrong. A moldy old sandwich like this one is anything but harmless. While there are some harmless kinds of mold - like on Camembert cheese - many molds are toxic. Furthermore, mycelium spores can trigger allergies. Through contact with highly toxic types of mold, humans with weakened immune defenses could even die as a result of an extended exposure.

Mold can also be useful: Fungi is able to break down carbon hydrates, fats and proteins - more efficiently than any other organism. Industry makes use of a genetically modified Aspergillus niger fungus, which produces enzymes that can be used in food processing and production of detergents - like a living factory.

"Botulus" is Latin for "sausage." If mistakes are made in the production of sausage, or if meat or vegetables get contaminated during canning, this can cause botulism. The bacteria Clostridium botulinum causes this life-threatening poisoning.

Clostridium botulinum thrives in anaerobic, or oxygen-free, environments. It produces the nerve agent botox - used among cosmetic surgeons to help smooth skin. But in food, it leads to paralysis. At first, certain body parts get paralyzed, resulting in symptoms like slurred speech. But later, also the muscles responsible for breathing and heartbeat freeze up - eventually resulting in death.

Fenugreek sprouts were a favorite among Germans trying to eat healthy - until 2011. That year, seeds contaminated with the bacteria Escherichia coli (EHEC) caused an outbreak that killed 53 people - hundreds more were sickened. EHEC produces a toxin that destroys intestinal wall cells, and later attacks brain and kidney cells. Cooking raw vegetables and meat kills the harmful bacteria.

But not all varieties of E. coli are dangerous. Inside the human large intestine, the bacteria are usually responsible for producing vitamin K - important for the development of bones and cells, and for blood coagulation. In biotechnology, the bacteria play a role in producing insulin and growth hormones. They can even be used for turning microalgae into alcohol-based biofuel.

Thousands of years ago, humans learned to use lactic acid bacteria - for the production of yoghurt, kefir, sourdough bread and cheese. Raw milk warmed to 20 degrees Celsius is heaven for bacteria: Within 10 hours, the milk will go sour. Milk fermented with the help of bacteria, however, can stay edible for much longer.

One of the many varieties of lactic acid bacteria are streptococci, which play a role in producing sauerkraut and fermented milk products. Although streptococci are everywhere - on humans, animals and plants - some of them are unhealthy. Some strains of strep can trigger tooth decay or sepsis, commonly known as blood poisoning.

Rod-shaped bacteria like Campylobacter and Salmonellae cause illness and death the world over. Undercooked beef, pork or chicken containing Campylobacter is a common cause of diarrhea wordwide. Typhus is the most dangerous form of salmonellae, triggering high fever, weak heartbeat and constipation. Every year, about 32 million people are sickened from typhus - mainly by drinking impure water.

Norovirus or stomach flu is transmitted person-to-person through traces of vomit or feces. Just 100 tiny norovirus particles are enough to infect someone. The virus can easily pass into the food chain via infected drinking water.

The practice of hand-shaking has been around for more than 2,000 years. It was documented in the times of antiquity, as portrayed on this ancient Greek flask. But the ancient Greeks, who thought illness was related to a imbalance of humors in the body and represented punishment from the gods, never made a connection between hand-shaking and disease.

Hand-shaking is believed to originate in how, for two strangers meeting for the first time, approaching each other with open right hands demonstrates a lack of weapons. On a neurochemical level, a proper handshake can release chemicals in the brain including the bonding hormone oxytocin, which can promote harmony and friendship. But researchers have found it's a significant way to spread disease.

Not only does hand-shaking pass along germs, it carries unspoken meaning - yet this can vary by culture. A firm handshake is positively perceived to show decisiveness in Western societies, while Eastern societies generally prefer weaker or "limp" handshakes to prevent imparting a sense of dominance. Regardless, whenever you shake hands, you come away with more than just a lasting impression.

Hand-shaking can transmit viruses like the cold or flu, parasites like scabies, and bacteria such as Staphylococcus (pictured above). Someone who has a cold could wipe their dripping nose, leaving mucus teeming with rhinovirus on that person's hand. When you shake hands with them and then touch your eye, you can catch that infection. Still eager to shake hands?

One surefire way to prevent the spread of disease, including through handshakes, is to wash your hands with warm water and soap on a regular basis. But many people simply don't bother: In one observational study, only two-thirds of men washed their hands after using a public restroom. Which might make you ask yourself: Do I actually want to shake hands with the next stranger I meet?

Prominent figures - including Bill Gates and Donald Trump - reportedly simply do not shake hands due to the disease factor. A person who is hand-shaking phobic could always carry around a small bottle of hand-sanitizer and constantly use it. But that person runs the risk of seeming obsessive and strange. Although there are some proposals for alternatives to shaking hands …

A recent study proposed banning handshakes from healthcare settings altogether. Hospitals could be made into handshake-free zones, for example. As more people come to understand the link between the handshake and the spread of disease, the "anti-handshake" movement even seems to be gaining momentum. But what could replace the glorious gesture?

A study has shown that exchanging greetings via fist bump, or a brief touch between the outer portions of two fists, transmits 90 percent fewer infectious organisms than the handshake. And with people like Barack and Michelle Obama setting the example, perhaps that could become the next big thing.