My body is made of the food I eat. Same with a bird.
A robin eats worms and reconstitutes them into its muscles and beak and feet and feathers. The leftovers come out the other end and become worm food. In this sense, the boundaries of what a bird is and what a worm is become fuzzy. In the same vein, I suspect that the boundaries of what and who I am are also less distinct than I usually imagine.