When Palestinian leader Yasser Arafat was reported to have slipped into a coma last week, the Israeli Air Force wasted no time scrambling several jets across the border into south Lebanon.
The overflights, which consisted of 11 aircraft and three reconnaissance drones, illustrate Israel's unease at the prospect of Palestinian refugees in Lebanon launching revenge attacks across the border should the ailing Palestinian leader die.
Those fears are shared on the Lebanese side of the border, with the government in Beirut as well as the Hizbullah organization wary of an Israeli backlash to Palestinian attacks.
The bottom line, say observers, is that Mr. Arafat's death could lead to instability in the camps in Lebanon as well as the Palestinian territories, creating an atmosphere for cross- border violence.
"Both sides are very concerned about what the Palestinians might do in the event of Arafat's death," says a senior security source in south Lebanon.
Indeed, at the end of October, suspected Palestinian militants fired a single Katyusha rocket into northern Israel. Security officials suspect that the attack was in response to the news that Arafat was dying and required treatment in France.
The Israeli Cabinet claimed on Sunday that four Katyusha rockets have been fired into Israel so far this year, and blamed Palestinian militants.
The Lebanese government keeps a tight leash on the estimated 350,000 Palestinians living in some 12 camps scattered throughout the country. But the poverty and squalid living conditions in these camps breed hopelessness and despair, making the Palestinians a potential source of instability.
For 40 years, Arafat has symbolized Palestinian statehood and he is revered by most of these refugees for his unstinting demand that they be allowed to return to their former homes.
Still, the Palestinian leadership in Lebanon is ruling out the prospect of revenge attacks along the border.
"It is not part of our political program to carry out operations whether, God forbid, President Arafat stays sick, or if he gets better," says Sultan Abul-Aynayn, the head of Arafat's Fatah faction in Lebanon.
Fatah is the most powerful Palestinian faction in the volatile camps in southern Lebanon, using funds controlled by Arafat to buy support. If the supply of funds dries up in the event of his death, Fatah may find its dominance challenged by more radical factions - a recipe for intra-Palestinian violence that could affect stability along the border.
Generally, however, Israel's principal concern from Lebanon is Hizbullah rather than Palestinian militants.
Although there are some 1,000 Lebanese troops deployed in the southern border district, Hizbullah fighters maintain control of the frontier itself, monitoring Israeli movements from a series of observation posts.
Hizbullah periodically launches attacks against Israeli troops occupying the Shebaa Farms, a strip of mountainside running along Lebanon's southeast border with the Golan Heights. But Hizbullah's anti-Israel actions are kept within a certain limit. Their intention is to needle the Israelis but not to provoke a heavy military response against Lebanon that could cause a backlash against Hizbullah's domestic popularity.
On Sunday, Hizbullah unveiled its latest means of rattling the Israelis by dispatching a reconnaissance drone across the border for the first time.
The drone, named Mirsad-1 (Arabic for "observer"), flew over several Israeli settlements, reaching Nahariya, five miles south of the border, before returning.
It was the first hostile penetration of Israeli airspace from Lebanon since 1987, when a Palestinian militant crossed the border by hang glider, landed outside a military base and shot dead six Israeli soldiers before being gunned down himself. Hizbullah said the drone was a response to Israel's repeated violations of Lebanese airspace, and pledged more flights.
"If Hizbullah sent a drone across the fence and brought it back again that will sting the Israelis no end," says a military attaché in Beirut.
In Israel, hard questions were asked yesterday about how the drone could reach as far as Nahariya without being spotted and shot down.
"A good number of senior Israel Defense Forces officers should be downright embarrassed by the Hizbullah drone that entered Israel's airspace in the western Galilee," wrote Amir Oren in Israel's English-language daily, Haaretz.
Ironically, however, if Palestinian militants do attempt to reach the border to launch attacks against Israel, the Israelis may find that they have an inadvertent ally in Hizbullah.
The Lebanese group is careful to protect its tactical control over the border, knowing that attacks by unauthorized parties can jeopardize the delicate balance between it and the Israeli military.
That balance has grown more fragile lately with Hizbullah, the Lebanese government, and Syria, which dominates its tiny neighbor, coming under intense pressure from the international community.
In September, the UN Security Council passed a resolution calling for Syria to cease interfering in the affairs of Lebanon, withdraw its estimated 14,000 troops, and dismantle Hizbullah and all Palestinian militant groups.
"Given the political environment, a Katyusha attack into Israel affects all three audiences - Syria, Hizbullah, and the Lebanese government," says Timur Goksel, a former senior adviser to the United Nations Interim Force in Lebanon. "It's very natural that Hizbullah would be against attacks by Palestinians, especially when firing single Katyusha rockets into Israel has no military or tactical value at all."
Bitter enemies they may be, but Hizbullah and Israel understand and observe the rules of the game that govern clashes along the border. That helps explain why Israel accepted that Palestinian militants were probably behind the recent rocket firing and chose not to blame Hizbullah.
"Hizbullah and Israel treat each other with silk gloves. It is a conflict that can be managed if there is a political will," the senior security source says. "The Palestinians, however, are volatile and pose a threat to everyone."