Because when they float in air they are non living but when they come in contact with a organism they started reproducing.
Shruti Pandey answered this
bcos we can not define virus as living or non-living so it is till now like biological puzzle.
Maitreyee Sethi answered this
because they lie on the borderline of living and non living organism. they can reproduce only in the host organism. when they are not in contact with a host organism they are non living . so there is a mystery about these viruses
Pradeep Ch answered this
because it is still not known to be living or non-living.
it is living and shows metabolism when inside a living organism and shows non-living characteristics when outside a living organism.
hope it helps@!!!
Ishan Goyal answered this
Viruses are considered as biological puzzles because there is always a misconception about considering them as living or non living
Preet Kamboj answered this
viruses r called biological puzzles becoz we cn't define them as living or non-living. viruses r bordr lines b/w lving ng non-living. howevr, dey reproduce inside d cells of organisms....