While slaughtering a fowl, it flapped its wings and the slaughterer lifted the knife, but quickly returned it to the animal's throat and slaughtered i

Answer

Since the knife was immediately returned to the animal's neck, the slaughtered animal is halaal. If there is no lengthy pause after the knife is lifted for whatever reason, the animal will be halaal. But a lengthy pause will render the animal haraam. Not returning the knife quickly will mean that the pause is 'lengthy'. In the case mentioned by you, the chicken was halaal.