Snake in the grass?

[kanie]

Test No. incompl/inter-15 "Popular Idioms (2) Garden", question 10

Don't trust him, he's a bit of a snake in the ..........

(a) grass
(b) flowers
(c) plants
(d) weeds

Test No. incompl/inter-15 "Popular Idioms (2) Garden", answer 10

Don't trust him, he's a bit of a snake in the grass.

Correct answer: (a) grass

Your answer was: incorrect
Don't trust him, he's a bit of a snake in the plants.
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why grass not plant? for my understnading Snake but come to gether with a plant

[Torsten]

A snake in the grass is a set phrase and means a treacherous person; a person who seemed to be a friend but turned out to be an enemy.
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