This is a singing sock puppet. There's a sensor inside that knows how wide his mouth is open, so he can sing up and down a scale. Open his mouth a little, he sings a low note; open wider, he sings a higher note; even wider, he screams at the top of his voice. And so on.
This one, with his beatnik scarf, likes early bebop and chromatic scales.
This rougher one likes Booker T and the MGs and wails in blues scales
The folky, green-brown patterned one likes Fairport Convention and pentatonic scales.
This one was made by Molly Anderson.
Blues, chromatic and pentatonic scales
These puppets can be tuned to sing in any scale or mode. At the minute their voices come from a small PD patch and some very basic electronics running on an Arduino, but they could also be rigged up to be a MIDI controller.
They can help illustrate relatively complex musical theory - such as the differences between blues, chromatic and pentatonic scales - through play and storytelling; this scale terminology is relatively advanced, and doesn't normally enter the school curriculum until children choose to specialise in music at GCSE level in the UK (ages 15 - 16).
A big thank you to Molly Anderson and Anne Brassier (who does a great line in characters called The Stitches, as well as wedding photography, by the way) for sewing and knitting the little guys for me.