....To test sustain.
Today for some reason I was listening in depth to the sustains on my guitars and I remember biting a music box (little turn wheel thing I purchased from hawkins bizarre for my girlfriend)
Any way you can basically feel it resonating in you skull kinda, so I strummed a few chords and single notes letting it ring and putting my top teeth down on top of the guitar. Anyway it works a treat and I could here some very unusual things that I didn't expect.
My Fret King (les paul) Mahogany+maple top had a very smooth consistent sustain whereas my Epiphone SG Mahogany body and neck had a more gritty kind of vibration.
Give it a try go onnnnn.....