How is claymation done?

I have always wondered about claymation, how do they do the small movements like blinking without wrecking the face/getting plasticine all over the eyeballs and wouldn’t a model slowly deform over time from being bent and if they do accidentally smoosh a model in the middle of a scene what happens? Do they have to reshoot the whole scene? And in movies like Chicken Run the models have a fair amount of detail on them, how do they deal with the little details getting disturbed?

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