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Bird contagion

This week, scientists report that New Zealand parrots can spread positive emotion, too — or at least behaviour that could indicate their state of mind. The researchers recorded the play calls of keas (Nestor notabilis) and played them back to groups of wild keas. When the birds heard the sounds, they played more vigorously and longer — certainly more than when they heard the calls of a South Island robin (Petroica australis). The calls did not, however, seem to act as an invitation to join existing birds at play. Some keas that heard them preferred to start their own play — typically embarking on feats of aerial acrobatics. With self-confessed anthropomorphism, the scientists suggest that the play calls of these birds act in the same way as infectious laughter in people (R. Schwing et al. Curr. Biol. 27, R213–R214; 2017). In its homeland, the playful kea is called the clown of the mountains. And as every good clown knows: cry and you cry alone. But laugh and the world laughs with you.

Solar power is contagious

adding one rooftop system on a block increased the average number of installations within a half mile radius by 0.44.
ecause he's constantly scrutinizing his traffic to figure out why certain posts do well and others don't, Mr. Zimmerman also keeps a running list of "hot" themes in his head. "It might be that right now, people don't care about stories about cats that much, and instead, sloths are more popular," he says. "So I'll have a rule—cats are out, sloths are in, focus on sloths because that's going to be your meal ticket." The whole process happens very quickly. "Within 15 seconds, I know whether an item is going to work," Mr. Zimmerman says. He usually has a headline ready to go a few seconds after that. "It's a biological algorithm," he says. "I've put myself into the system—I've sort of become the system—so that when I see something I'm instantly thinking of how well it it's going to do." Indeed, Mr. Zimmerman says he can no longer tell the difference between stories he finds interesting and stories that will be popular. "If it's not worth posting then I'm not interested," he says.
The first person reading the comment was 32 percent more likely to give it an up vote if it had been already given a fake positive score. There was no change in the likelihood of subsequent negative votes. Over time, the comments with the artificial initial up vote ended with scores 25 percent higher than those in the control group.