At a Paris train station, the zap of a pigeon getting electrocuted on the tracks was enough to send some jittery people scurrying for cover, in the aftermath of the devastating attacks on Nov. 13.
And in Brussels, the city center is often deserted as armed soldiers patrol tourist sites amid repeated government warnings that a terrorist attack is "serious and imminent."
Some experts say it will take months for Europeans to psychologically adapt to life after the Paris attacks and warn that certain government measures intended to reassure people may backfire, creating instead the impression of cities under siege.
"We go about our daily lives and every so often they're punctuated by something outrageous like a terrorist attack on an average Friday night," said Dr. David Purves of the British Psychological Society. "After that shock, something that is highly statistically unusual may suddenly feel much more likely to happen."
Purves said that measures meant to reassure people, like machine gun-toting soldiers and closed subways, might actually feel like the opposite.
"In a time of uncertainty, we may interpret these signs of safety instead as reasons to be fearful, like why would we need armed soldiers unless there was danger?"
Belgian university student Lotte Achterberg said she could certainly do without the now-ubiquitous soldiers guarding Brussels.
"It's not a nice feeling to see them everywhere with their big guns," she said on a sunny Thursday morning in the capital's cobblestoned Grand Place. "They look like bad guys with their faces all covered even if they are maybe very nice people, she said. "I'm too scared to talk to them. "
Some said the ongoing maximum threat alert in Brussels - in place since Saturday and set to last until at least Monday - may be counterproductive.
"People cannot be highly vigilant forever," said Neil Greenberg, a professor of military mental health at King's College London. Unless the government provides a better explanation of what's going on, he said Belgians' attentiveness may fade. "If nothing happens - if no huge plot is discovered or arrests are made - people will think it's an overreaction and the government will lose credibility."
Greenberg said it typically takes several months for people to move on after a traumatic event, citing the response of Londoners after the July 7, 2005, bombings, where four suicide bombers on the public transport system killed 52 people. In the weeks after the attacks, many people said they planned to stop taking the subway. But six months later, the number of subway users had actually risen, he said.
In Brussels, regional authorities have introduced a 50-euro-a-day "danger premium" for bus drivers heading to the capital, a move some say is sending the wrong signal to drivers and passengers who may already be nervous about traveling.
Others said it was important for people who survived traumatic events to learn how to interpret possible triggers like loud noises in crowded places, and to recognize the nearly infinitesimal chances of a repeat attack in the following weeks.
"We don't want to reinforce the Chicken Little belief that the sky is falling," said Frank Farley, former president of the American Psychological Association. He said most people in Paris and Brussels now likely have elevated anxiety levels and that major changes to daily life would likely not only be unnecessary, but play into the hands of extremists. "The terrorists might be high-fiving themselves for being able to interfere with how the Western world works."
Farley said the upcoming holiday season should help with the recovery process.
"Focusing on the positive will be a big help," he said. "The holidays should outweigh the horrors in Paris and start to take the sting out of that experience."