One thing I feel that may be important to add would be that even though an audience may be silent and not very creactive no matter what you show them, they could still be extremely impressed.
For example, when I visited some of my family over in Sweden, I performed a little for me aunt. She seemed completely uninterested (with the sort of "yeah... great..." type reaction). Apparantly however, the next day, while she and my mother were out shopping, the topic of "those little spongeballs that jumped everywhere" kept coming up. And I mean over, and over again. She had actually one of the most entertaining things she had seen in a while.
Anyhoo, my point is that if it's one specific audience that's giving you the reaction.. it may just be their way of reacting. This may, or may not apply to you of course
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Alright, on the topic of advice... ehm, I suppose you could try to use some more audience interaction. As soon as a spectator gets involved they become just that little bit more emotionally attached to the effect.
Just my 2 cents on the topic