Such a simple thing, really: An egg cracked. Then another.
Two tiny hawks wriggled free, teetering feebly in their nest on a third-floor ledge of the Franklin Institute.
But a webcam was watching and, through it, thousands of viewers. The all-day spectacle yesterday high above the busy streets kept people around the world glued to their computers, from One Logan Square to Missouri to England.
"It's nature taking its course, right here in front of us," said Dennis Wint, the institute's president and chief executive officer.
Midday, the male brought a dead rat or mouse - the staff couldn't tell - and much later the female ripped off some shreds and fed the first chick.
About that time, the third chick began to hatch.
And it's going to get better.
Within a day or two, the tiny chicks will start moving around more, said Doug Wechsler, director of visual resources for ornithology at the Academy of Natural Sciences, just across the square.
Things could even get dramatic. One of the riskiest times in a bird's life is right after hatching. Will the parents be able to feed the nestlings adequately? Keep them warm?
A significant predator - the horned owl - seems unlikely in downtown Philly. But you never know.
Months ago, the whole thing seemed so improbable.
That was when the hawks began building a nest, but several times it blew down. Then a building crew fastened a board in place to widen the ledge, and the nest stayed.
It just happened to be in front of a window, which made it possible to mount a webcam with live streaming.
By mid-March, three eggs had been laid. The staff anticipated they might hatch as early as April 6. But the days went by, and nothing happened.
Finally, yesterday morning, a hole appeared in one of the eggs, and online chat took off.
"Around 9:45 Eastern there was some scrooching around and I saw two intact eggs to the right and definite hole-making in the egg to the left," one viewer wrote. "Watching seriously now!"
By midday, at least 1,300 viewers were watching at any given time.
"This is the collision of nature and technology," marveled Jeffrey Kahn, a real estate investor in Center City.
His wife had called midmorning to make sure he caught the action. "Now, all of a sudden, the whole world can be in Philadelphia looking in a hawk's nest."
Sure enough, in Sheffield, England, Christine Frankland continued a vigil that had begun a few weeks ago. "I have nearly burned a few family meals watching this," she wrote in an e-mail. "It's not every day you get to see something like this."
Outside St. Louis, former midwife Alice Trask "was cheering when I saw one of the babies and they moved."
Back in Philadelphia, Micah Watson, 12, and his brother Noah, 15, who are home-schooled, took their studies near the computer so they could keep tabs.
"We learned the word anthropomorphism today," said their mother, Deborah. "It's fascinating to see what life is like for the bird and not transfer our expectations."
Truth to tell, watching eggs hatch - and getting infrequent views at that, since most of the time the action was hidden under one or the other adult - may not seem so exciting in a world intent on instant gratification.
The birds don't have the cachet of, say, being an endangered species. Hawks are common.
What hooked viewers was the sheer fact that they could watch nature unfold. "Here's one little life," Kahn said.
In California, Brad Hunstable, president and founder of Ustream.tv, which is running the video, watched with amazement - not just the birds, but also the tally of viewers. Since the eggs were laid, he has tracked 100,000 individual viewers.
Ustream was started to help soldiers overseas keep in touch with their families, but nature videos have really taken off.
The hawks are rating almost as high as the video of a great white shark dissection not long ago. (Most wanted to see what was in its stomach.)
Then there's arguably the most famous video of all - the cam that followed Hunstable's puppies. It got to 30 million viewers in 30 days and, the last he checked, added up to 850 years of viewing time.
"Content like this is a dream come true," he said.
Watch the chicks via the Franklin's webcam: http://go.philly.com/earthEndText