Pirates of the Caribbean: On Stranger Tides

Captain Jack Sparrow (Johnny Depp) travels to London to locate the person who has been impersonating him. The impostor has reportedly been recruiting a crew to search for the legendary Fountain of Youth. First Sparrow rescues his former first mate, Joshamee Gibbs (Kevin McNally), who is about to be hanged, though the two are captured. Jack is brought before King George II (Richard Griffiths), who wants him to guide an expedition to the Fountain before the Spanish find it. Heading the expedition is Jack's old nemesis, Captain Hector Barbossa (Geoffrey Rush), now a privateer in service to the British Navy after having lost Jack's ship, the Black Pearl, as well as his leg.Jack escapes, and is found by his father, Captain Teague (Keith Richards), who warns Jack about the Fountain's tests. Jack soon discovers that the impostor is Angelica (Penélope Cruz), his former lover and daughter of the ruthless pirate Blackbeard (Ian McShane), who possesses supernatural powers and practices voodoo magic. Jack is forced to join Blackbeard's crew and to lead them to the Fountain. Meanwhile, Gibbs, who memorized, then destroyed, Sparrow's map, barters with Barbossa to lead him and his crew to the Fountain.Aboard Blackbeard's ship, the Queen Anne's Revenge, Jack learns that the Fountain's water must be drunk simultaneously from two silver chalices once belonging to Juan Ponce de León. The person drinking from the chalice containing a mermaid's tear has their life extended, while the other person dies, their years of life drained from their body. Blackbeard intends to use the Fountain's power to circumvent his fated fatal encounter with a one-legged man, and sets a course for Whitecap Bay. There he traps a mermaid that Philip Swift (Sam Claflin), a captive missionary, falls in love with and names Syrena (Àstrid Bergès-Frisbey). Blackbeard then sends Sparrow to retrieve the chalices from de León's grounded ship. Sparrow arrives finding only Barbossa: the Spanish have already taken the chalices.Barbossa's only wants revenge against Blackbeard for having captured the Black Pearl, forcing Barbossa to amputate his own leg to escape. He and Jack plot to defeat Blackbeard, then steal the chalices from the nearby Spanish camp. Meanwhile, Syrena, who returns Philip's love, is tricked into shedding a tear, which Blackbeard collects, then leaves her to die while forcing Philip to go with him. Sparrow returns with the chalices and Gibbs, who he had reunited with while helping Barbossa. Jack negotiates with Blackbeard to return his confiscated magical compass and to free Gibbs in exchange for the chalices and his leading them to the Fountain. Blackbeard agrees, and Gibbs departs with Jack's compass.At the Fountain, Blackbeard and his crew are attacked by Barbossa and also the Spanish, sent by their king to destroy the Fountain, believing its power is an abomination against God. After an intense battle, Barbossa stabs Blackbeard with a poison-laced sword, but Angelica is also wounded by it. Barbossa claims Blackbeard's magical sword, and assuming command, leaves with Blackbeard's crew. Philip, mortally wounded, escapes and returns to free Syrena. After finding the chalices that the Spaniards tossed into deep water, Syrena gives them to Sparrow, then retrieves the dying Phillip, taking him underwater to heal him.Angelica intends to sacrifice herself for her father, but Sparrow deceives them, and Angelica unknowingly drinks from the chalice containing Syrena's tear, thus killing Blackbeard and saving her. Although they declare their love, Jack, knowing she may avenge her father's death, strands her on an island, intending for a passing ship to pick her up. Jack then finds Gibbs, who used Sparrow's compass to locate the Revenge and retrieve all the captured ships that Blackbeard had magically shrunk and bottled, including the Black Pearl. The two head off, hoping to find a way to return the Pearl to its original size.In a post-credits scene, Angelica, still on the island, finds Blackbeard's voodoo doll of Sparrow, which has washed ashore.

Question: What is special about Blackbeard's sword?
Answer: It is laced with poison