In this video, the presence of ankle clonus is being tested. Clonus is defined as a series of rhythmic, involuntary muscular contractions induced by sudden passive stretching of a muscle or tendon. To test for ankle clonus, the leg and foot should be relaxed and the knee and ankle placed in a slight flexed position. With one hand, the examiner stabilizes the lower leg and holds the foot with the other. The examiner then quickly dorsiflexes the foot whilst maintaining slight pressure on the sole. Unsustained clonus fades away after a few beats and may occur in normal individuals. Sustained clonus, as in this case, is when clonus persists as long as the examiner continues to exert slight dorsiflexion pressure on the foot. Sustained clonus is always pathological and is an upper motor neuron sign.