I have known it in a few dogs (my friends BC is terrible for it).
She will hunt for anything (she used to pull threads out of the carpet as well) but especially hair to make herself sick. Oddly her sister behaves in the exact same way (although they have been brought up very differently) and no other dogs in the households (both are multi dog) practise this behaviour.
Both are coming up to 5 and have never had any ill effects from it.
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