Suicide bombers claimed by the Islamic State of Iraq and the Levant (Isis) just hit Shia mosques in Saudi Arabia two Friday prayer-times in a row. This, obviously, presents a threat to the kingdom. But it is not just an external threat from jihadi extremists entrenched in Syria and Iraq. It is above all an internal challenge: for a country ideologically fuelled by the Wahhabi interpretation of Islam that, like Isis, brands Shia Muslims as idolaters and apostates. The House of Saud, under its new monarch, King Salman, will need to do something about extremist ideas as well as acts. After the first of the two bombings, both in Saudi Arabia’s eastern province where the kingdom’s Shia minority is concentrated, a video posted online by local activists showed a policeman inside the blasted mosque standing over the remains of the bomber, apparently saying “God rest his soul” — the soul of the murderer, not his victims. While it is impossible to verify the circumstances of the film, reported by Reuters, there is little doubt about the feelings of the blood-bespattered worshippers screaming “let God not rest his soul” at the policeman.