Well, if they were non-living, they would not
really have characteristics of living things.
Living things use energy, grow, and reproduce
(sexually and asexually) unaided.
There may be things that look like there are
non-living because they may not be humans or
animals, but still are. Or a creature that does
not move may be mistaken for non-living.
There are two different types of cells:
eukaryotes and prokaryotes. The main differences
are that prokaryotes have no nucleus, are
unicellular, don't have a true membrane, and have
no mitochondria (the powerhouse of a cell).
So may be some people may confuse prokaryotes
to be non-living even if they are living.