Vibrating your head blurs your vision (try taking a metronome or substitute, striking it, and then touching your teeth with the stem while looking at something with a well defined edge or ridge: the picture will become slightly blurry).
I wonder what's the frequency dependence. I have two (nonlocking) forceps that, when measured with my phone's accelerometer, give similar amplitudes of ~50Hz+harmonics and resp. ~60Hz+harmonics. Maybe I'm placeboing myself, but it seems to me that the blur from 50Hz one is significantly larger.
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I guess I can bust out my bone conduction speaker that I have somewhere and try using that to have a continuous frequency variability (without messing with play-doh).
But also, the volume of the sound I was hearing wasn't that high, so either I failed to notice the same effect when I was hearing louder lowish frequency sounds, or this is more pronounced because eyes are "closer" to teeth than ears.