This is an old Lenni Lenape tradition and legend.
“A long time ago a Lenni Lenape man was struck with an illness that would bring him his death. His name was Kolawil which meant Beautiful Head. Kolawil went deep into the forest and lay upon a boulder to die. Briefly he slept. When Kolawil awoke he was surrounded by a circle of animals. Each animal gave Kolawil its own personal medicine. The snake hissed and slithered across Kolawil giving him his own medicine. The turtle said nothing and gave Kolawil his own boiled medicine. The hawk screeched and gave the dying man his medicine of feather. The wolf howled and licked Kolawil giving him his own medicine. After all of the animals gave of their medicines Kolawil felt better and was cured! The animals then spoke and said “Two legged one, in a similar way you will cure your fellow kind.” The animals used the smoke, water, earth and fire of life to surround the man with a vision. He gathered the pieces of the animals that they left and created a circle from tree limbs and plants. He placed upon the circle the pieces left for him in a sacred way. The medicine shield glowed with power and he brought it back to his lodge. So Kolawil was given Mantoallumund. He became a great Medicine Man and healer of his people and so eventually learned how to use this gift for all life. So it was that the true ideal of healing was made, to give from the heart without asking back, without prejudice, without taboo, and without fear. And it was because the animals gave freely of their medicine without prejudice of another kind, taboo of doing what needed to be done, fear of the unknown, or requiring anything but purity and trust. Life gave freely of its medicine.”
The legend says Kolawil made a medicine shield from the animals, the plants and their power which he called Mantoallumund (Great Spirit Medicine). Traditionally this was given to someone that you wanted to send power, enlightenment, “medicine”, luck or good energy to.
It is tradition among many Native American people including the Lenni Lenape to leave a gift for the deserving one to find. Gifts were not given they were left in places where you would find it. If you found a gift then you deserved it and so thanks was not required or expected. If you did not deserve it you would not have found it. This was tradition.