Most of the year, Canadians living in the United States look, talk and act so much like their neighbors that their nationality draws no attention at all. Autumn is a season of danger, though, when the mask of assimilation can be ripped off, forcing some Americans to face the unnerving, if fleeting, realization that Canada is an entirely different country.

All it takes is one mention of Canadian Thanksgiving.

The first reaction is typically laughter, as if this were another fine example of the Canadian sense of humor. Then comes disbelief. Finally, when it emerges that the holiday is celebrated on the second Monday in October, there may be a suspicion that on the other side of the border, time does not behave in the same way.

“It tends to domino into other big holidays,” said Kathryn Borel, a television writer in Los Angeles who grew up in Toronto and Quebec City. “They’ll really carefully ask you: ‘Do you celebrate Christmas on the same day? Do you celebrate — Easter?’ You can see it messing with their paradigm, like, if Thanksgiving is different, what else is different?”

A state of total innocence about Canadian Thanksgiving is easy to maintain in the United States, where the holiday gets about as much attention as the half-birthday of the youngest child in a family of 12. For one thing, it happens on Columbus Day, so eyebrows are not necessarily raised if somebody slips back to Saskatoon to spend the weekend with the family.