Most people have seen bullies in action, making life miserable for others. Their targets often escape the intimidation relatively unharmed, but sometimes it is too much to bear. That can be true whether the victim is a 12-year-old girl or a 136-kilogram American football player.

A member of the Miami Dolphins left the National Football League team recently because he was repeatedly insulted and threatened by a teammate, Richie Incognito. Many fans were disgusted by details of Mr. Incognito's expletive-filled voice mail and text messages, while others defended his behavior as a natural part of a rough-and-tumble sport.

Some people are astonished that Jonathan Martin, who is 1.95 meters tall, "could actually be emotionally damaged by taunts from a teammate," the columnist Timothy Egan wrote recently in The Times. "Can you possibly hurt a hulk with words?"

Based on his own experience playing football in high school, Mr. Egan argues that you can. He was smaller than the other guys and had a big, unruly head of hair that made him stand out. His teammates taunted him. "Did it hurt? Yes it did," he wrote. "I knew very well what it felt like to give so much to a game and have people who were part of it, his teammates, hurt him."

Bullies aren't all men. The Times reported recently that scientists had made big strides in understanding aggression by young women.

"The existence of female competition may seem obvious to anyone who has been in a high school cafeteria or singles bar," John Tierney wrote, "but analyzing it has been difficult because it tends to be more subtle and indirect (and a lot less violent) than the male variety."

Researchers found that women were more likely to make mean comments about other women if they saw them as competition for male attention. In an experiment, a group of female college students reacted negatively when a woman wearing a low-cut blouse and a short skirt entered the room, while they barely noticed the same woman dressed in a T-shirt and jeans.

But in perhaps one difference between the sexes, instead of confronting the woman directly, the others made fun of her once she left the room.

"Women are indeed very capable of aggressing against others, especially women they perceive as rivals," said Dr. Tracy Vaillancourt, a psychologist at the University of Ottawa.

For those on the receiving end who are young or otherwise vulnerable, the damage can be tragic. In September, a 12-year-old girl in Florida named Rebecca Ann Sedwick killed herself after other girls bullied her online. She went to an abandoned cement plant, climbed to a platform and jumped.

"Rebecca became one of the youngest members of a growing list of children and teenagers apparently driven to suicide, at least in part, after being maligned, threatened and taunted online," The Times reported. And teenagers aren't just using Facebook or Instagram to pick on one another. New applications appear constantly, making it difficult for parents to keep tabs on their children's activity. Rebecca's mother, Tricia Norman, didn't know her daughter was receiving messages that said: "You're ugly" and"Can u die please?"

"You hear about this all the time," Ms. Norman said of cyberbullying. "I never, ever thought it would happen to me or my daughter."

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(China Daily 12/01/2013 page9)