One bottle was all it took.
Protests in Ferguson, Mo., were peaceful Tuesday as night began to fall, offering a reprieve from nearly 10 straight days of unrest since the fatal police shooting of Michael Brown. Officers stood idle as people chanted and marched in circles near West Florissant Avenue. "So far, so good," tweeted St. Louis Alderman Antonio French, who has been there for days.
But when the clock struck midnight, the mood shifted.
A water bottle was launched from a crowd of protesters at police, according to CNN. Officers started to approach the crowds, and some protesters began to act defensively almost immediately, CNN's Steve Kastenbaum reported from the scene. "Not tonight!" shouted some protesters as tensions began to rise.
At least 47 people were eventually arrested.
The rapid change in mood reflects the persistent fragility that has come to define Ferguson since Brown's death on Aug. 9 and that has thrust the St. Louis suburb to the forefront of a national conversation about race, police militarization, and press freedom.
Protesters know by now how quickly the situation can escalate. In an apparent attempt to diffuse the situation, a small cohort of community members attempted to create a human barrier between the police and the rest of the crowd.
Most of the protesters had gone home by that time. Dozens of reporters remained, some of whom tweeted photos of police arresting people at the scene.
A week ago, a relatively calm Thursday night led some protesters and police to feel optimistic about future demonstrations. But that feeling quickly dissipated, and the weekend brought perhaps the most dramatic clashes since Brown's shooting.
On Wednesday morning police did not deploy the heavy-handed crowd-control tactics that had defined previous nights of protests, such as tear gas. But authorities appeared to use pepper spray on demonstrators, and, reportedly, on at least one journalist.
"Tonight, we saw a different dynamic," Missouri Highway Patrol Capt. Ron Johnson said early Wednesday at a news conference. "Protest crowds were a bit smaller, and they were out early. We had to respond to fewer incidents than the night before. There were no Molotov cocktails tonight. There were no shootings."
Still, the security situation in Ferguson remains extremely delicate. Daylight may bring peace, but nighttime carries uncertainty.
"We're gonna have to do something different," said Johnson at the scene, according to The Washington Post's Wesley Lowery, who was arrested by police last week.
Despite the apparent arrests, Tuesday night marked a drastic departure from the chaos that erupted late Monday, culminating in the arrests of 78 people.
This story was updated with last developments Wednesday morning.