There's been a foreign type of plant life that have grown and rapidly sprouted from underneath the earth within your planet. One day, you're living your life as you usually do, and don't notice the leafy roots that move on their own along the ground, creeping quietly. You feel a needle sharp pain in your leg all of a sudden. You look down, and see a thick black thorn sticking out of there.

As you carefully remove the thorn, you don't realize you've been marked to be found later on.