The Blippoo Box
Ah! The fabled Blippoo Box. There are many adjectives that describes the sonic character of the "bent by design" box : organic, unique, chaotic, unpredictable, etc...
But you really have to play it once to have a small idea of its potential.
Rob also offers a banana version of the Blippoo Box for those who want to interact with their Buchla/Serge/Banana systems.
There is a great page from Richard Scott's website about the Blippoo Box, including an album and videos with and without the Benjolin.
Hans Tammen has an instructive page about the Blippoo Box too with videos of different applications.
But the most complete and deeply instructive article about the Blippoo Box is in the Leonardo Music Journal issue #19 of 2009. Be sure to read and own it. Wonderful explanation about the concept and the design of the box.
Here is the flowchart of the Blippoo Box.
Also Youtube has some great gastric sounds. Check for more.