How about this for an odd bit of kit?
It's called an echo cornet, the idea is that by engaging the 4th valve the sound bypasses the bell and enters the echo chamber, mimicing the sound of an echo. Very cool for messing about on.
[VIDEO]http://www.youtube.com/watch?v=5Nv8PT-uPXw]YouTube - Echo Cornet[/VIDEO]
Wow, that's very odd. Doesn't seem all that useful, though--the echo effect sounds too strong, to me.