We have heard of "laugh tracks". So throughout history, there have been people available for hire or use who offer clapping at performances. It is to help boost enthusiasm in the audience for the performance. Here is more info about what a claque means.

"…a theatre or individual could order anywhere from a handful of well-placed plants to a large audience full of enthusiastic supporters to fill out empty seats or bolster the desired reaction to a début play or performance in order to influence subsequent reviews."

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