Thirukkural- On Virtue- Hypocrisy-Kural-277

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Like the 'Kunri' seed, there are some people who shine red all over,But are inwardly black as the nose of the same seed.

Kunri is a small, hard and bright-red seed with a black nose, which is used as the smallest unit for weighing gold and so very familiar to the people of Tamil Nadu. The idea that the heart and mind of vicious people is black, is a common one, and has been used by Kambar in the following line:

"Maikaru manathoru vanjan"

Shakespeare brings out the sense of this poem differently in the telling expression, 'A goodly apple rotten at the Core'.