Pebble throwing. Vitriol. Protests at hospitals. Is it just ‘anti-vaxxer mobs’ or a new brand of Canadian political violence?

If it had been just the pebbles, that would not have been far outside the realm of expectation for a Canadian election, said Amarnath Amarasingam, a Queen's University expert in extremism who's been watching the crowds protesting Liberal Leader Justin Trudeau with trepidation.