In English it’s common to say, “I know this town like the back of my hand!” While we may know our towns really well, how well do we actually know our hands? Maybe not quite as well as we think, said a scientific study.

Matthew Longo and his team from University College London studied the left hands of100 people. With their hands placed palms down under a board, Longo’s team gave the instruction to point to their knuckles (关节) and fingertips with a marker. How did they do? Not that well.

“People think their hand is wider than it actually is,” said Longo. He said they also seemed to think their fingers were shorter than their true lengths. People were most accurate (准确的) when finding their thumbs, but became less accurate with each finger, up to their pinkies (小指).

“It is connected to our sense of position,” explained Longo. Humans know where different parts of our bodies are, even if we can’t see them. “It tells us whether a joint (关节) is straight or not,” said Longo. “We also need to know the distances between our joints,” he went on. Our brains know the sizes and shapes of our bodies from the maps they make for themselves. “This experiment tried to find those maps,” he said.

Maybe maps don’t need to be perfect. But why aren’t our brains more accurate? Longo said our brains “see” areas based on our sense of touch, with the stronger the sense of touch in a specific body part, the bigger that body part seems. An example is our lips. As they have more nerves (神经) than our noses, our brain’s map shows our lips are bigger. The same thing can happen with body parts that have a lot of nerves. If you’ve ever had something stuck in your teeth, it probably felt huge! That’s because our tongues also have lots of nerves.

When it comes to keeping off extra pounds, watching what we eat may not be enough—we have to keep an eye on our food’s packaging, too. Half the world is expected to be overweight by 2035. In addition to overeating and lack of exercise, the scientific community is exploring another factor that may contribute—eating products packaged in plastic.

For a study published last year, researchers at the Norwegian University of Science and Technology set out to determine what chemical compounds (化合物) exist in 34 common plastic items that touch things we eat, such as yogurt cups, juice bottles, candy packages, and plastic wrap used for produce and cheese, as well as items often found in kitchen.

Of the 55,000 chemicals the researchers found in these items, only 629 were identifiable, which influence our bodies’ ability to regulate weight, troubling health effects. “We’re quite certain that there are many chemicals in plastic products that impact metabolism (新陈代谢), but we just couldn’t identify all of them,” Martin Wagner, a study co-author said. Strikingly, Wagner and his colleagues found that a third of all the common products they tested contain chemicals that cause the adipogenic (生脂的) process. Although we are exposed to them daily, most of these mystery chemicals are unknown, unstudied and unregulated.

For years, experts have been warning against plastic food containers, particularly for hot or oily foods which may make the plastics unstable and increase the risk of chemical leaching (渗出). As one of them, Wagner argues that we need to start reducing our exposure to plastic without waiting for more slow-moving research to prove that the plastics in our food, products, blood and organs are risk factors for bad health outcomes.

Really, reducing our plastic exposure should be our overall goal. When we think about cutting junk out of our diets, the criminals shouldn’t just be candy and soda—plastic needs to go, too.

If you’ve ever thought that dogs seem to know when people are stressed, you were right. Scientists in Ireland ran an experiment which showed that dogs can tell the difference between the smell of a person when they’re relaxed and when they’re stressed.

Researchers at Queen’s University Belfast, led by scientist Clara Wilson, worked with four dogs. They taught the dogs to use a special smell-testing device with three openings. The scientists used treats and rewards (奖励) to train the dogs to find and signal the correct opening. Over time, the dogs were given harder and harder smelling jobs. The final goal was to see if they could smell stress in the breath and sweat of a person.

So the researchers collected breath and sweat samples (样品) from 36 different people. They got samples when the people were calm, and also when they were stressed. To stress people out, the scientists asked a really difficult math problem, and forced people to do it in their heads quickly. And they weren’t nice about it. They kept telling the people to hurry up, and didn’t give them any help. That lasted for three minutes. Then the researchers collected two more sweat and breath samples. They also asked the people about their level of stress, and measured their heart rates and blood pressure. Most people said they felt very stressed. On average, the heart rate increased from about 91 beats per minute to about 105 beats per minute.

The scientists used one of the stressed samples, along with two clean pieces of cloth, to train the dogs to find the stressed smell. Then came the challenge- the dogs had three choices: a sample from a calm person, a stressed sample from that same person, and a clean piece of cloth. In all, the dogs did 720 of these tests. They correctly identified the stressed sample about 94% of the time.