Definition: In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.
Input: Article: The Man of Many Secrets -- Harry Houdini -- was one of the greatest American entertainers in the theater this century. He was a man famous for his escapes -- from prison cells, from wooden boxes floating in rivers, from locked tanks full of water. He appeared in theaters all over Europe and America. Crowds came to see the great Houdini and his "magic" tricks. Of course, his secret was not magic, or supernatural powers. It was simply strength. He had the ability to move his toes as well as he moved his fingers. He could move his body into almost any position he wanted. Houdini started working in the entertainment world when he was 17, in 1891. He and his brother Theo performed card tricks in club in New York. They called themselves the Houdini Brothers. When Harry married in 1894, he and his wife Bess worked together as magician and assistant. But for a long time they were not very successful. Then Harry performed his first prison escape, in Chicago in 1898. Harry persuaded a detective to let him try to escape from the prison, and he invited the local newspapermen to watch. It was the publicity  that came from this that started Harry Houdini's success. Harry had fingers trained to escape from handcuffs and toes trained to escape ankle chins. But his biggest secret was how he unlocked the prison doors. Every time he went into the prison cell, Bess gave him a kiss for good luck -- and a small skeleton key, which is a key that fits many locks, pass quickly from her mouth to his. Harry used these prison escapes to build his fame. He arranged to escape from the local prison of every town he visited. In the afternoon, the people of the town would read about it in their local newspapers, and in the evening every seat in the local theater would be full. What was the result? World-wild fame, and a name remembered today. 
 Answer: his unusual ability and a skeleton key

According to the passage, Houdini's success in prison escapes depends on   _  .