Jack's sword is a sword that was coated with poison, so that when it made even the slighted cut on someone's skin, they would face a swift and certain death. The sword was forever lost in the giant's castle when Jack and James went on a mission to slay the giants and steal their gold.
Before the Curse
Jack is left for dead. ("Tiny")
Prince James is seen making out with his new girlfriend, Jacqueline, before moving her over to the bed. Before the situation can progress, King George walks in to tell his son that a giant has been spotted roaming the outer-village. Jack mentions that she has always wanted to do battle with one, but George tells them not to kill it as they stand to gain something from it. James and Jack later approach the giant, Anton, and the latter gives him a piece of mushroom from Wonderland that she was given for slaying a Jabberwockey. Anton eats it and shrinks to human-size and James and Jack treat him to a drink at the tavern he was previously inspecting. As James goes to get them some drinks, he is hassled by a knight and Jack explains to Anton that the kingdom is in great debt to another kingdom and if they don't pay it soon, the kingdom will be burnt to the ground, Anton offers to give up his treasure in order to save the kingdom. Jack thanks him, calling him a hero. Jack and James later arrive at the top of the beanstalk in the giants' castle and reveal that they were conning Anton the entire time in order to steal the giants' magic beans. The pair of them kill all of Anton's brothers but are unsuccessful in getting any beans. Jack is stabbed by Arlo and begs for James' help as she dies, however, James bags all of the treasure that he can gather and flees the castle, telling Jack that he has a kingdom to run and that she understands. ("Tiny")
After the Curse
Emma keeps the giant under threat. ("Tallahassee")
At the base of the beanstalk, Killian tells Mulan, Aurora, Emma who actually is James' niece and Snow, James' sister-in-law, that it's the last beanstalk in all the lands and the Giant at the top is the last of his kind because of Jack. Later, in the Giant's castle, Emma and Hook discover Jack's skeleton, in the treasure room. Emma is astonished when she see Jack's sword, saying it is a toothpick. However, when the Giant attacks them, Emma proceeds to collect Jack's sword from her skeleton's hand. Emma turns to face the giant, sword in hand, as it continues to walk towards her, at the right moment, Emma slices the sword through the air, chopping through the tripwire as she does so. The cage on the ceiling tumbles down, landing on the giant, entrapping him beneath it. Emma keeps the Giant under threat of the sword which she realizes is dipped in some sort of poison, hence why he is so afraid of it. When the Giant accuses her of being a killer, Emma assures him he's wrong, as she does not use the sword and allows him to live. ("Tallahassee")