A boat party in an exclusive area of Long Island (search) Sunday night was interrupted -- when a severed human hand mysteriously dropped out of the sky onto the deck of a boat, police said yesterday.

The bizarre incident occurred in the water just off the Lawrence Village Marina (search), where a group of boats had gathered to have a party.

One owner was in the cabin when "he heard a noise, goes out to check and finds the hand on the rear deck of the boat," said Nassau Detective Sgt. John Azzata. "At this point, we don't have a clue where it came from. It's a mystery."