Imagine extras from 'The Muppet Show' doing 'Whose Line Is It Anyway?' That's the concept behind Brian Henson’s long-running 'Puppet Up!' improv comedy show.

While puppets have long appealed to moppets — upbeat shows filled with marionettes and felt figures have a whimsical way of eliciting giggles from youngsters — puppetry as an art form has long had an ...