[odo1242]

chomping at the bit

[danpalmer]

Actually it was originally "champing" – to grind or gnash teeth. The "chomping" (to bite) alternative cropped up more recently as people misheard and misunderstood, but it's generally accepted as an alternative now.

[odo1242]

I see

[kortilla]

It’s actually accepted as the primary now and telling people about “champing” is just seen as archaic.