Saturday's attack, the deadliest on Saudi soil in more than a decade, marked a sharp escalation in the Yemen war. Riyadh backs the internationally recognised government against the Houthis, who captured swathes of the Red Sea coastline in a lightning offensive last month. The Saudi-led coalition has vowed a firm response, but what options are on the table? We discuss this with Dr Nawaf Obaid, Senior Research Fellow in the Department of War Studies at King's College London.