Once every two weeks, 20 people gather to laugh, even if they don't feel like it - especially if they don't feel like it. They are cancer patients at Sheba Medical Center, Tel Hashomer. Their laughter can be heard bursting out of the hospital's movie theater and rolls down the corridors to the specialists' offices. "Laughter is contagious," their facilitator, Ruthie Hai, explains, as she encourages the group to laugh louder, to force themselves. "Go with what you feel," she exhorts the patients, seated on the upholstered chairs with their eyes closed.

Suddenly, Hai bursts out with a great guffaw over nothing, and is greeted with a roar in response. But not by everyone. "Laugh, laugh," she urges a patient who is merely smiling. "Laugh, let it loose," she commands. He breaks out in a little giggle. "Good, you're moving along!"

Hai has been "treating" patients at Sheba's oncology department for a year now. She embraces them, dances with them, plays them music and makes them laugh even if they are troubled and their bodies ache from chemotherapy. This afternoon, she plays the song "Together" ("Yahad") by Gaya and asks people to dance.

Yehuda Hudra, 79, from Neveh Monoson, has come with his wife Ida. About two years ago, he was diagnosed with cancer in his right lung, which had to be amputated. He rises from his chair, dances a bit and then sits back down to rest. He tires quickly but never misses his laughter yoga session. "I come here for some air," he says. "It opens up the lung I have left. I learn to laugh and it really makes me feel good." Yehuda's wife Ida says that since he was taken ill, his mood has not been good. "At first he didn't want to come here, but I made him come so he would forget his troubles a little. When we're at home, I see him sitting in the living room in a bad mood. I apply the techniques I learn here. I come up to him and surprise him. I laugh out loud right in his face. He laughs back; the mood changes and he feels different," Ida says.

Gabriel Sa'id, 46, a married father of seven from Safed, has been undergoing chemotherapy and arrives at the session with an infusion in his arm. Ruthie greets him with a great big laugh. "She taught me to laugh like a broken ignition of a car," Sa'id says. "I learned here that sadness doesn't lead anywhere. I learned to leave sadness aside and to laugh more. Sometimes I dance with myself," he says.

Hannah Tzarfati comes from Rishon Letzion to the laughter yoga class every chance she gets. She says it has taught her to deal with her frustration and pain. "The workshop gets me out of the house. I learned that the house is depressing. The most important thing is to get out as much as possible, to get around. Not to be closed up inside," she adds.

The head of oncology at Sheba, Prof. Raphael Katan, says cancer can develop in both sad and happy people. And yet, on more than one occasion he has found himself referring patients to Ruthie Hai's workshop.

"It's a good influence on patients' moods and it's important to us that their quality of life be good, even if they are going through a difficult period," Katan continues. "Unfortunately, laughter doesn't improve their medical condition, but it certainly improves the atmosphere."