What is the meaning of 'chomping at the bit'?

[Oinas]

English Language Tests, Intermediate level

ESL/EFL Test #318 "English Slang Idioms (39)", question 2

"I think that this class of police cadets will do very well. They are all chomping at the ......... to get out there and fight crime," the instructor said to the captain.

(a) carrot
(b) food
(c) wood
(d) bit

English Language Tests, Intermediate level

ESL/EFL Test #318 "English Slang Idioms (39)", answer 2

"I think that this class of police cadets will do very well. They are all chomping at the bit to get out there and fight crime," the instructor said to the captain.

Correct answer: (d) bit
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What is the meaning of "chomping at the bit"?

[Beeesneees]

The original, traditionally correct version is 'champing on the bit'. However, 'chomping...' has been in use for so long that it is also considered correct.

One part of a horse's harness is the 'bit' - this is the mouthpiece, used to control the horse.
'Champing' or 'chomping' is biting down loudly and vigorously - as a horse might do on his 'bit' when he is noticeably eager, especially a horse such as a race-horse before a race, when tension is greatest.

So 'champing/chomping at the bit' = obviously very eager to do something.
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Cheers m' dears!