What does this idiom mean: "She gets on her high horse"?

[Pupil]

Test No. incompl/inter-56 "High and Low", question 8

It's always the same when you break one of the rules of the office, she gets on her high ......... and starts shouting at you.

(a) camel
(b) pony
(c) donkey
(d) horse

Test No. incompl/inter-56 "High and Low", answer 8

It's always the same when you break one of the rules of the office, she gets on her high horse and starts shouting at you.

Correct answer: (d) horse

Your answer was: n/a
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What does it mean?
she gets on her hight hourse
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the more we learn
the less we know

[Alan]

It means to be very arrogant.
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English as a Second Language
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