[El Sordo]

"I did see about 7 cops - with guns - surround and take a guy into custody in one of the Metro stations for something."

He probably was overheard muttering an ethnic slur.

[mountaineer]

I should have mentioned the guy I saw the Paris cops take into custody was black. He was gesticulating wildly, in an attitude of "hey, I didn't do nothing," and the gendarmes weren't having any of it. His companion, also black, started to intervene when he realized he'd be next if he didn't shut up, so he did.