Last week's unprecedented missile attack by Iran-backed Houthi rebels in Yemen, on Islam's holiest city of Mecca, was a stark wake-up call that Israel may soon find itself caught in the cross-hairs of an apocalyptic confrontation between Sunni and Shia in the Middle East.
The ballistic missile was intercepted before it could reach its alleged target.
But what was sobering was how Saudi Arabia - which has established close (if unofficial) intelligence and military ties with the Jewish state to confront a potentially nuclear-armed Iran - chose to frame its condemnation by reference to Israel.
Brigadier General Ahmed Asiri, spokesman for the Saudi-led coalition that has been bombing Yemen for the last 18 months, said that the missile was similar to those provided to Hizbollah in Lebanon by Iran.
While the Houthis' slogans include "Death to Israel!", their targeting of Mecca, he added, proved the real object of their military wrath was Sunni Muslims, who should not be seduced by the Houthis' claims to be committed to Israel's destruction.
Here, then, was an acknowledgement that, despite years of vitriolic anti-Shia propaganda from its state-controlled media, Saudi Arabia's new alliance with Israel has quickly turned into its achilles' heel.
That bodes ill for Israel and its efforts at increasing cooperation with Sunni-majority Arab countries - a fact far from lost on Iran.
Indeed, just days before the Houthi missile, a senior Iranian military official, Major General Mohammad Ali Jafari, was busy accusing Israel and Saudi Arabia of plotting to stir insurrection inside the Islamic Republic.
And former Iraqi Prime Minister Nouri Al-Maliki, who handed Baghdad to his fellow Shia in Tehran on a platter, told an Iran-sponsored conference in the Iraqi capital that the campaign to liberate Daesh-occupied Mosul would be only the first step to liberating other cities. "We are coming Raqqa, we are coming Aleppo, we are coming Yemen," he promised - singling out the Sunni-Shia flash points in the region.
Iran and its Shia allies and proxies have every reason to feel triumphant.
The regime of President Bashar Al-Assad will remain in Syria; the election in Lebanon of staunch Iranian ally Michel Aoun has legitimised Hizbollah as the main national political party there; the US has called for an end to the Saudi-led bombing of Yemen, meaning the Houthis will emerge victorious; and post-sanctions Iran continues to play the West like a fiddle while cultivating ties with an Egyptian regime that also officially supports Assad and has been cast adrift by the Saudis.
Given this worst-case scenario of Iranian regional hegemony, for Israel increased cooperation with Saudi Arabia must feel like small compensation - and not least because, as the backstabbing rhetoric after the Mecca missile incident illustrated, when push comes to shove, the Wahhabi kingdom itself will unlikely think twice before playing the anti-Israel card.
