It is a truth universally acknowledged, but not often stated, that clinical judgement is insufficient to exclude subarachnoid haemorrhage with acceptable certainty. Why wax lyrical about the minutiae of the clinical assessment? Perhaps the neck was slightly stiff. Perhaps one pupil was slightly sluggish. What of it? Ultimately, when the patient came in complaining of a first episode of acute severe headache, we all knew that a CT was inevitable. And, to boot, since we were sufficiently suspicious of subarachnoid haemorrhage to perform a CT, and in the absence of a compelling alternative explanation, we would be negligent not to then follow-up the normal scan with a lumbar puncture after 12 hours to look for xanthochromia. Is this intellectual bankruptcy? Wise heads on the post-take ward round will cluck knowingly. 'Ah, rushed in with a scan, did we?' How infuriating! The luxury of the normal CT scan report is enabling of maddening arrogance. The same is true of troponin. A 6...