I used to put my teeth against the neck of my bass guitar when tuning it sometimes, to hear the notes better (when unplugged, of course). It really works, especially when tuning with harmonics as you can physically feel the "phase" from two almost-the-same-frequency-but-not-quite notes.
You look like an idiot though, get yourself an electric tuner it's like £10.
You look like an idiot though, get yourself an electric tuner it's like £10.