Jamie Morton is the NZ Herald's science reporter.

Strange But True: Is the 5-second rule real?

Scientists have disproven the five-second rule. Photo: Christin Lola / Fotolia
Scientists have disproven the five-second rule. Photo: Christin Lola / Fotolia

Scientists have disproven the idea that it's okay to scoop up food and eat it within a "safe" five-second window.

"The popular notion of the 'five-second rule' is that food dropped on the floor, but picked up quickly, is safe to eat because bacteria need time to transfer," said study author Professor Donald Schaffner, of New Jersey's Rutgers University.

"We decided to look into this because the practice is so widespread. The topic might appear 'light' but we wanted our results backed by solid science."

The team dropped watermelon, bread, bread and butter, and gummy sweets on stainless steel, ceramic tile, wood and carpet surfaces for less than a second, five, 30 and 300 seconds.

Watermelon had the most contamination and gummy candy the least. Carpet had very low transfer rates compared with those of tile and stainless steel, whereas transfer from wood was more variable.

They found that moisture, the type of surface and contact time all contributed to cross-contamination and, in some instances, the transfer began in less than one second.

Although they found the five-second rule is "real" in the sense that longer contact time
resulted in more bacterial transfer, it also showed other factors, including that the nature of the food and the surface it fell on, were of equal or greater importance.

A selfie a day keeps the blues away

Regularly snapping selfies with your smartphone and sharing photos with your friends can help make you a happier person.

Researchers at the University of California conducted exercises using smartphone photo technology and gauging users' psychological and emotional states, finding that daily taking and sharing of certain types of images can positively affect people.

The study's goal was to understand the effects of photo-taking on "self-perception", in which people manipulated positive facial expressions; "self-efficacy", in which they did things to make themselves happy; and "pro-social", in which people did things to make others happy.

University of California researchers have shown that regularly taking selfies has benefits for happiness. Photo: Steve Zylius / UCI
University of California researchers have shown that regularly taking selfies has benefits for happiness. Photo: Steve Zylius / UCI


The project also involved three types of photos to help the researchers determine how smiling, reflecting and giving to others might affect users' moods.

These included a selfie, to be taken daily while smiling; an image of something that made the photo taker happy; and a picture of something the photographer believed would bring happiness to another person.

Participants were randomly assigned to take photos of one type.

"Our research showed that practicing exercises that can promote happiness via smartphone picture taking and sharing can lead to increased positive feelings for those who engage in it," study lead author Yu Chen said.

"The good news is that despite their susceptibility to strain, most college students constantly carry around a mobile device, which can be used for stress relief."

Angry person? Your walk will give you away

The way people walk can give clues to how aggressive they are.

That's according to UK researchers from the University of Portsmouth's psychology department who assessed the personalities of 29 participants, before using motion capture technology to record them walking on a treadmill at their natural speed.

The study, which compared this technology with findings of personality tests, found that the exaggerated movement of both the upper and lower body indicated aggression.


University of Portsmouth researcher Liam Satchell works with a participant in a new study that has drawn a link between walking style and aggression. Photo: University of Portsmouth
University of Portsmouth researcher Liam Satchell works with a participant in a new study that has drawn a link between walking style and aggression. Photo: University of Portsmouth


"When walking, the body naturally rotates a little; as an individual steps forward with their left foot, the left side of the pelvis will move forward with the leg, the left shoulder will move back and the right shoulder forward to maintain balance," lead researcher Liam Satchell said.

"An aggressive walk is one where this rotation is exaggerated."

People were generally aware there was a relationship between swagger and psychology, Satchell said, but the new findings provided empirical evidence to confirm that personality was indeed manifested in the way we walk.

"We know of no other examples of research where gait has been shown to correlate with self-reported measures of personality and suggest that more research should be conducted between automatic movement and personality."

Who says trees can't feel?

Some trees can tell when a deer is nibbling at them.

German researchers have been able to find that young beeches and maples can recognise precisely whether a branch or bud has been purposefully nibbled off by a roe deer - or just randomly torn off by a storm or other mechanical disturbance.

The saliva of the animals gives them the signal: if a deer feeds on a tree and leaves its saliva behind, the tree will increase its production of salicylic acid.

This hormone, in turn, signals to the plant to activate a kind of defence mechanism, by increasing the production of specific tannins.


Carolin Seele of Leipzig University and Stefan Meldau of Max-Planck-Institute for Chemical Ecology collect buds in a study showing some trees can defend themselves against deer. Photo: Bettina Ohse
Carolin Seele of Leipzig University and Stefan Meldau of Max-Planck-Institute for Chemical Ecology collect buds in a study showing some trees can defend themselves against deer. Photo: Bettina Ohse

These substances are known to influence the feeding behaviour of the deer, causing them to lose their appetite for the shoots and buds and move on.

The saplings also boost concentrations of other plant hormones to enhance the growth of the remaining buds to compensate for the lost ones.

"Following this initial fundamental research, it would now be interesting to also examine other tree species and their defence strategies against roe deer," lead researcher Bettina Ohse said.

"If some turn out to be better defended, these species could possibly be used more in forests in the future."

The science of... shark bites

Sharks have a big reputation for their teeth.

The ocean predators use their buzz-saw mouths to efficiently dismantle prey, ranging from marine mammals and sea turtles to seabirds and - as Hollywood likes to remind us - an occasional human.

Each of the more-than 400 species of sharks on the planet has a unique tooth shape - some are simple triangles, and others are deeply notched or spear-shaped.

But despite the variety, scientists haven't detected a difference in how different shark teeth cut and poke tissue.


Researchers have attached shark teeth to reciprocating saw blades to see how the big ocean predators feed. Photo: University of Washington
Researchers have attached shark teeth to reciprocating saw blades to see how the big ocean predators feed. Photo: University of Washington

A recent US study sought to understand why shark teeth are shaped differently and what biological advantages various shapes have by testing their performance under realistic conditions.

The researchers affixed three types of shark teeth to the blade of a reciprocating power saw, then cut through thick slices of Alaska chum salmon at a speed that mimicked the velocity of head-shaking as a shark devours its prey.

They found different teeth cut differently, and some species' teeth, such as those of tiger sharks, dulled more quickly than others, meaning they had to replace their teeth more often.

The authors say the study could shed further light on the feeding patterns of different sharks, which could boost efforts to conserve them.

- NZ Herald

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