Knocked the stuffing out

[Igor]

Test No. incompl/inter-54 "Lots of Stuff", question 10

It came as a great shock to him when he heard the news and quite ......... the stuffing out of him for days.

(a) hit
(b) pulled
(c) knocked
(d) threw

Test No. incompl/inter-54 "Lots of Stuff", answer 10

It came as a great shock to him when he heard the news and quite knocked the stuffing out of him for days.

Correct answer: (c) knocked

Your answer was: incorrect
It came as a great shock to him when he heard the news and quite hit the stuffing out of him for days.
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What does it mean "knocked the stuffing out"
Thank you very much

[Alan]

Frightened him
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English as a Second Language
You can read my ESL story Word Story: Health