Survival Island

The film revolves around Jack Ryan (Billy Zane) and Jennifer (Kelly Brook), a rich couple who are yachting in the Caribbean during Christmas. One of their crew is the handsome Manuel (Juan Pablo Di Pace), who is cursed by his angry ex-girlfriend as he prepares to leave on the yacht. He is clearly bothered and has a difficult time fulfilling requests for the crew and guests. After the captain confronts him, Manuel quits and throws down a rag as he storms out of the galley. The rag lands on a gas flame and causes the entire yacht to catch fire. The captain is unable to control the blaze with a fire extinguisher so they abandon ship. Their lifeboats are capsized by a storm later that night and everyone becomes separated.
Washing up on a deserted island, Jennifer is completely alone until she sees the body of the captain in the water. As she attempts to resuscitate him, Manuel appears and also unsuccessfully tries to revive the man. They bury the captain and, under Manuel's guidance, set out to build a shelter and find food. Eventually, Jack also turns up on the island. Although things go smoothly for a little while, Jack eventually suspects Manuel of having desires on his wife and declares the man his enemy, promising to ruin his life once they get off the island. Manuel responds that Jack had better get home soon, because he can ruin Jack's life right there on the island. This puts Jennifer in the uncomfortable position of her loyalty to Jack conflicting with the realization that they both need Manuel's help to survive. A proud man, Jack insists that he can provide for them both, but it quickly becomes apparent that he cannot. Jack and Jennifer's relationship also starts quickly deteriorating.
Jack steals Manuel's goggles to go fishing one day and when Manuel discovers this, he threatens to kill Jack. Jennifer attempts to get him to calm down and, in a fit of passion, they have sex. Afterwards, Manuel reveals that he has loved Jennifer from the moment he first saw her, but it is also clear that this is a way for him to hurt Jack. When Jack returns, Jennifer accidentally hints at him what had happened and Jack furiously rejects her. He breaks up with her and drags her by the hair to Manuel's hut so she can live with him.
While fishing another day, Jack finds a boat on the ocean floor. He drags it to shore and attempts to repair it. Later, Manuel proposes Jennifer a midnight swim and as they start having sex, Jennifer gives Manuel the idea of stealing the boat so they can get away together from the island. They plan to do so while Jack is out fishing. However, they do not get far before the boat begins to sink and they realize that Jack's plan all along was for them to take the boat and drown. They are forced to swim back to the island and to Jack, who attacks the now-exhausted Manuel with a spear. The following day, an intense fight sequence ensues, interwoven with scenes of Manuel's ex-girlfriend performing a voodoo ceremony. The scene climaxes when Jennifer pins Jack to the ground, attempting to kill him with his own knife. Manuel, with Jack's spear stuck in his back, picks up a heavy rock with which to crush Jack. He loses his balance and falls backward, impaling himself on the spear, to Jennifer's horror. Simultaneously, the voodoo girl impales his effigy on a spike.
One year later, a yachting family drops anchor near the island and explores it, discovering Jennifer asleep in her hut. She, still somewhat distraught over Manuel's death, leaves with them, but does not mention that her estranged husband is also on the island. Jack, who is fishing, sees her leaving on the yacht and calls out, but Jennifer, who had also stolen his lighter so he could not make anymore fires, ignores him out of revenge and the family inside the boat cannot hear him. Jack is abandoned on the island and his eventual fate is left ambiguous.

Question: What did Jennifer use to attempt to kill Jack with?
Answer: His own knife.