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These will form the main shape of the nest, and are much easier to work with than hard, short twigs. You can use straw, long grass, vines, willow fronds, bendy reeds, or seagrass found outdoors or at a garden supply store. Raffia is another good option, obtainable from a craft supply store. If Mexican feather grass grows in your area, grab a clump of it and pull your hand upward to remove a handful of hairy seeds clinging together. Once you have enough seeds, clump them into a ball and make a nest shape by sticking your thumb into it.
Find long, flexible plant stems.