Kural - 585

Of unsuspected mien and all-unfearing eyes,
Who let no secret out, are trusty spies

Explanation
A spy is one who is able to assume an appearance which may create no suspicion (in the minds of others), who fears no man's face, and who never reveals (his purpose).

Tamil Transliteration
Kataaa Uruvotu Kannanjaadhu Yaantum
Ukaaamai Valladhe Otru.