This is a neurological examination finding that indicates an upper motor neurone lesion of the examined extremity.
To perform it, hold the patients middle finger between your thumb and index finger. The patient must relax. With your thumbnail press on the patient’s nail and whilst pressing move downwards until your nail clicks over the end of the patients fingernail.
A positive Hoffman response is the other fingers especially the index finger, flexing after the click.These stills are taken from the video below.