GutCheck Arrow Wipe Indicator allows instant confirmation of a vital or gut shot. Simply wipe down the full length of the arrow shaft making sure to get all surfaces around the shaft. Blood will show up on the wipe and will not react with the indicator formula and, therefore, visually indicates a â??cleanâ?쳌 vital hit was made. Should the arrow pass through the acid-containing digestive tract of the animal, the indicator will immediately change color. This will allow the hunter to determine how the hit animal should be pursued.