Although an icicle may grow in size over time, it is considered non-living because there is no metabolic activity present. An icicle is composed of crystallized molecules of water, which is a non-living, inorganic substance. A primary characteristic of living things is their ability to carry on complex biochemical reactions involving both inorganic and organic molecules. These reactions enable the organism to perform life functions essential for their growth and reproduction. When taken together, these biochemical reactions are known as metabolic activity.

This bird may best be described as a heterotroph that may eat insects and is more closely related to a robin than to an earthworm. Woodpecker finches are common in the Galapagos Islands. They have evolved a nutritional behavior that allows them to probe tree wood for borrowing insect larvae, similar to true woodpecker species native to New York State. Because they consume other living things (insect larvae) for food, woodpecker finches are classified as heterotrophs (other feeders). Because the woodpecker finch is a bird, it is considered to be more closely related to other species of birds, such as the robin, and less closely related to segmented worms, such as the earthworm.