snake in the grass

snake in the grass (plural snakes in the grass)

1. (idiomatic) A hidden enemy.
   • 1906, Horatio Alger, Randy of the River, ch. 6:

     "I trusted him too much from the start. He has proved to be a snake in the grass."

   • 1914, William MacLeod Raine, A Daughter of the Dons, ch. 5:

     "Is he not here to throw us out—a thief, a spy, a snake in the grass?"

   • 2008 Nov. 21, Bruce Crumley, "Which Woman Will Lead France's Socialists?," Time:

     Following her presidential defeat, Royal stunned many observers by publicly dumping Socialist Party leader François Hollande — her companion and the father of her four children — and announcing she'd seek his post during the current election. To some, that made Royal the symbol of the strong, modern woman in politics; to others, it cast her as the classic snake in the grass.

• backstabber