It has a puncturing needle driven at great speed by a very small magneto-electric engine on the penhandle.

The resident, now looking off-balance himself, did his thing with merciful skill, extracted the lumbar puncture needle, filled a vial full of golden spinal fluid, and left the procedure room shaking his head.

Contact between the side of the lumbar puncture needle and a spinal nerve root can result in anomalous sensations (paresthesia) in a leg during the procedure; this is harmless and patients can be warned about it in advance to minimize their anxiety if it should occur.