Eavesdropper

In the German Alps it is believed that the cattle have the gift of language on Christmas Eve. But it is a sin to attempt to play the eavesdropper upon them.

She's a bit of an eavesdropper, innit?

[…] the Japanese Ministry of Defence rang the bell and informed the world's press about the Tokyo Express — the ironic Japanese nickname for the constant flow of Soviet flying eavesdroppers in Japanese airspace.