Lai and colleagues1 compare 786 migraineurs and 98 patients with cluster headache with respect to cranial autonomic symptoms (see page 1116). Explicitly, they asked about lacrimation, conjunctival injection, nasal congestion, rhinorrhoea, eyelid oedema and forehead/facial flushing. They identified one or more cranial autonomic symptoms in 56% of migraineurs and 95% of cluster headache patients. In general, migraineurs had less features, they were less prominent, less consistently related to attacks and more likely to be bilateral compared with patients with cluster headache. As with most things, the more you look at them the more you see, some would say even imagine, or perhaps imaginatively extract. Why would a neurologist be interested in yet another acronym—CAS (cranial autonomic symptoms)? I will try to briefly set out the anatomy and physiology that leads to these symptoms, their differentiating value comparing trigeminal autonomic cephalalgias (TACs) and migraine, and the direct clinical implication of that difference. Whatever one thinks of acronyms, the presence and implications of the symptoms are useful for clinicians and ultimately helpful in managing patients.