Answer:We aren't shown exactly how the Joker pulls off any of his stunts, it's part of the mystery of his character. In order to pull off the two that you mentioned, the Joker would need meticulous planning and impeccable timing. It seems impossible to pull off either crime without anyone noticing but that's kind of the point. The Joker is apparently prepared for any contingency.
Answer: We aren't shown exactly how the Joker pulls off any of his stunts, it's part of the mystery of his character. In order to pull off the two that you mentioned, the Joker would need meticulous planning and impeccable timing. It seems impossible to pull off either crime without anyone noticing but that's kind of the point. The Joker is apparently prepared for any contingency.
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