Dyna and Tillo
Dyna and Tillo are the two birds who have a nest in Things Betwixt. To reach their nest, leave the bonfire in the area, and go through the tunnel to the tutorial section. Enter the first door on the left and follow it all the way to the top. Now hug the left wall as you exit the top doorway and you will see a large nest.
Stand in the nest, then go to your inventory and select one of 4 items listed below. Use the Leave option to place it on the ground and the birds will thank you and give you something in return. This can be done as many times as you want, so long as you have one of the 4 prerequisite items.
Items
Leaving one of the four following items has a chance to reward you with another item. The system is random, so it might take some time to get the desired item.