Something suspicious fell off its back (5)
I believe the answer is:
lorry
'back' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for lorry that I've seen before include "HGV" , "Load-carrying vehicle" , "Large motor vehicle for transporting goods" , "Transport vehicle" , "Heavy goods vehicle" .)