You have a splinter. You just had to walk barefoot through the soft green grass, and now have a sliver of wood embedded in your foot. Duct tape to the rescue.
Splinters can be difficult to remove. Especially if they are smaller. Tear a piece of duct tape large enough to cover the area where the splinter is located. Place the duct tape over the splinter, being sure to cover it on all sides. Press the duct tape firmly down. Lift the duct tape away. This should lift the splinter out also. Be sure to clean and bandage the wound.