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we use our hands to put fries in the bread and then eat the sandwich with our hands. I think each one eat with his/her way that make them a comfortable.

I live in France. When I eat at MacDonalds, I eat fries with my hand but in my house when my fries are in a plate with beside a steak , I eat the fries with my fork.

I spent 40 years in the US. One time, I saw a British coworker eat fries with a knife and fork. I assume (but have no evidence) that the British are taught to not touch food with their hands. I have spent some time in France, and one of my "living-in-France" advice books mentioned that the French do not touch food with their hands.

Like Anna, I live in France. I generally use my fork when I eat fries but at McDonald's I use my hand (that's the only place where I do that). It's like eating pizzas, people often use a knife and fork - at the restaurant for example.