Extract the answer to the following question from the movie plot. If the question isn't answerable, please output "Can't answer". Question: what happens while superman is busy? Title: Superman Movie plot: Superman is sent to Earth by his parents just as the planet Krypton blows up and is later raised as Clark Kent by a farm couple. They discover that he has great powers so they send him off to use his powers to help those in need. After his foster parents die, the Man of Steel heads to Metropolis under the bespectacled guise of Kent and joins the staff of the Daily Planet in order to be close to the news. Soon after he is sent out to get the scoop on a new rock that a man has found that he calls Kryptonite and Clark passes out, the director thinks that he died but when he sat up, he was wrong. Then and there Superman discovered that his weakness is Kryptonite. Whenever emergencies happen, he responds in his true identity as Superman. This first serial revolves around the nefarious plot of a villain who calls herself the Spider Lady.
The answer to this question is:
he finds out his weakness is kryptonite