Grave Grass

It is not known whether Grave Grass grows naturally or is created by the presence of Dhar, but it is a common menace in graveyards, battlefields, or any other place rich with its primary food source—rotting flesh. On the surface, only a light cover of soft green grass is visible, but underground, the extensive root systems grow bunches of five-foot-long barbed spikes of incredible hardness, coiled like springs. When the plant senses pressure on the grassed areas above, it shoots these spikes out of the earth at blinding speed, impaling the unwary. Tomb robbers and Vampire hunters have tried to develop systems for determining which pieces of grass contain these deadly pressure points but with little success. Others simply let their dogs or lackeys walk ahead of them, for once the spring has been released, the grass is harmless.

Source
pg. 138
 * Warhammer Fantasy RPG 2nd ED -- Night's Dark Masters