What looms suddenly in your rearview mirror and is past you in a streak on the stone slip of a darkened street is crime-fighting Israeli-style: two men, dressed in black, bent low on a dark motorcycle, the one behind with his automatic rifle angled off his back, the bike darting quick as a bat.
A moment later up ahead, near the Ben Yehuda shopping area in the center of Jerusalem, a man is up against a wall, dressed in clothes that resemble what a Hasidic Jew would wear, but in a faintly raffish way that doesn't quite square with the sober probity of Hasidism. The backseat rider from the motorcycle is frisking him; the driver, still atop his bike, is reaching for the man's identification.
The man is eventually let go but not before he is closely questioned. He has just had his first, and he hopes his last, brush with the motorcycle unit of Yasam, an elite police unit.
In a city that has experienced war, terrorism, and its share of crime, the sight of these fast-moving patrols elicits little reaction. But for newcomers, the first impression is of something straight from a thriller or a gritty science-fiction tale.
Their low-slung KLE 550 motorcycles are powerful and highly maneuverable, the right specs for threading the clogged and narrow streets of this edgy city at high speed.
And speed was of the essence one night in the summer of 2002, when, at the height of the intifada, a Palestinian militant started firing automatic weapons at pedestrians on busy Jaffa Street. A two-man Yasam team, blocks away, heard the gunfire and raced to the scene.
Jumping off their bike, the officers confronted the gunman. Shots were exchanged as pedestrians flattened on the sidewalk; the gunman was killed.
Tzvika Hassia, the superintendent of the Jerusalem Yasam force, said 24 members of his 80-person unit "ride and fight from motorbikes and are meant to answer (to) special criminal or terrorist acts quickly, getting to where cars can't go." Israel is divided into six police districts, and each has a Yasam unit.
To even be considered for the Yasam unit, applicants must have served in one of Israel's military combat units and been highly rated. Given that Israel has had precious few days without conflict, that means nearly all have seen action.
Their dark clothes, their no-nonsense bikes, and a certain common swagger make them stand out in a country where many people wear uniforms and carry guns.
"In my opinion, they are awesome," said Ya'akov Brod, 24, a security guard for the Coffee Bean & Tea Leaf coffeehouse on Jaffa Street near Zion Square. "They are like the best of the best. Although they are police - if you ask me - they are part of the army."
On the narrow, twisting streets of hilly Jerusalem, accidents on the bikes are unavoidable.
"At the speeds we go, there is no way to avoid them," said Alon Weinstein, 31, who joined Yasam 2 ½ years ago after serving in an army reconnaissance unit.
"You have to like motorcycles. You live your life on them," he said, grinning and cradling his M-16. "But this is the best place to be."
The men on each team rotate as the driver and the firepower on the back. They carry M-16s and 9mm handguns. While the units were created - beginning in Jerusalem - during the 1990s to deal with terrorism and then the intifada and the upsurge in suicide bombers, they are no less busy since the intifada gave out and the suicide attacks became rare, a police spokesman said.
While declining to give statistics, spokesman Micky Rosenfeld said, the units are still stopping militant Palestinians trying to commit terrorist acts. Much of the units' activity on that front takes place without publicity, he said.
In Arab East Jerusalem, feelings toward the Yasam unit are not as warm as those held elsewhere. In fact, none of the shopkeepers interviewed along Salah Eddin Street had a good word for the unit, calling it anti-Arab.
"No one messes with Yasam, especially the ones on the bikes," said Amr Sandouka, 25, who works in the family business selling electronics equipment. "They are rude, violent, and have a license to kill."
"It is shocking to hear those words," Rosenfeld said. "Yasam is the most advanced operational unit in the police that has stopped tens of terrorist attacks and hundreds of criminal acts."