You're out to dinner. The food is delicious and the service is fine. You decide to leave a big fat tip. Why? The answer may not be as simple as you think.

Tipping, psychologists have found, is not just about service. Instead, studies have shown that tipping can be affected by psychological reactions to a series of different factors from the waiter's choice of words, to how they carry themselves while taking orders, to the billl's total.

Even how much waiters remind customers of themselves can determine how much change they pocket by the end of the night.

“Studies before have shown that mimicry （模仿）brings into positive feelings for the mimicker, "wrote Rick van Baaren, a social psychology professor. "These studies show that people who are being mimicked become more generous toward the person who mimicks.

So Rick van Baaren divided 59 waiters into two groups. He requested that half serve with a phrase such as, "Coming up!" Those in the other half were instructed to repeat the orders and preferences back to the customers. Rick van Baaren then compared their takehome pay. The results were clear-it pays to mimic your customer. The copycat （模仿者）waiters earned almost double the amount of tips to the other group.

Leonard Green and Joel Myerson, psychologists at Washington University in St Louis, found the generosity of a tipper may be limited by his bill. After research on the 1,000 tips left for waiters, cabdrivers, hair stylists, they found tip percentages in these three areas dropped as customers' bills went up. In fact, tip percentages appear to plateau （稳定期）when bills topped $100 and a bill for $200 made the worker gain no bigger percentage tip than a bill for $100.

"That's also a point of tipping," Green says. "You have to give a little extra to the cabdriver for being there to pick you up and something to the waiter for being there to serve you. If they weren't there, you'd never get any service. So part of the idea of a tip is for just being there."

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Delicious and sweet bananas are full of vitamins, trace elements and nutrients. It is the raw material of many healthy foods, too. 【小题1】? Usually ends up in the garbage cans, right? There are, however, three uses of banana skins that you may have never thought of.

The first one is to cover for grilled chicken. Chicken baked on the grill (烤架) is very tasty and healthy. 【小题2】, you should take its skin off. In this way, however, the meat remains unprotected over the heat and fire and can dry out easily. If you cover the chicken with banana skin, it will protect the meat from drying out. 【小题3】.

Are you looking for a quick solution to refresh your tired skin or a budget friendly and natural antiwrinkle treatment?【小题4】. Place a small banana skin under your eyes, apply it on your face for 5 minutes and then wash it off, which might help reduce wrinkles on your face and relieve swollen eyes.

The last one is that banana skins are cheap and simple teeth whitening【小题5】. Simply rub your freshly washed teeth with the inside of the banana shell every day for about 2 minutes. Salicylic (水杨酸的) acid in bananas gently causes teeth to become white, effectively removing dirt.

Scientists already knew that gulls (海鸥) prefer food that has been touched by people, but it was unclear how well they could draw on their observations of snacking humans to find similar bits of food while foraging (觅食).

In the latest work, Feist, a biologist at the University of Sussex and her colleagues taped green (salt and vinegar) and blue (cheese and onion) packets of crisps to bricks and placed them a few metres from gulls on an otherwise clear patch of Brighton beach. The scientists then backed 5 metres and filmed the birds’ behaviour. In some cases, the researchers simply looked at the camera, while in others they pecked (啄) a green or blue bag of crisps.

When the scientists sat quietly without snacking, less than a fifth of gulls approached the crisp packets placed nearby. But when the researchers were snacking on crisps, 48% of the birds hopped over to check out the packets. Nearly 40% of such approaches ended with gulls pecking at the crisp packets, and of these, 95% were directed at the same colour packet as the scientist was eating from. “It is impressive because the evolutionary history of gulls wouldn’t have involved humans,” said Feist.

The work suggests that there is work to do to reduce tension between humans and urban gulls. The impact of “do not feed the birds” signs might, for example, be improved by adding “…and don’t let them see you eat, either”.

“It is likely that simply stopping the public from directly feeding gulls may not be enough,” Feist said. “They are still able to observe what we eat and that would inform their ability to target waste, litter and so on.”

Dr Goumas, an expert on gulls at Exeter University, said: “This study shows that we aren’t only drawing gulls’ attention to where food is, but they also learn about the type of food we’re eating. Knowing this may have implications for how we reduce negative interactions between humans and gulls, as we seem to be unconsciously teaching gulls to explore new food items.”