<Tr> <Td> US Billboard Hot 100 </Td> <Td> </Td> </Tr> <Tr> <Td> US Cash Box Top 100 </Td> <Td> </Td> </Tr> <Tr> <Td> Zimbabwe Singles Chart </Td> <Td> </Td> </Tr> <Table> <Tr> <Th> Chart (1966) </Th> <Th> Rank </Th> </Tr> <Tr> <Td> US Billboard Hot 100 </Td> <Td> 54 </Td> </Tr> <Tr> <Td> US Cash Box Top 100 </Td> <Td> </Td> </Tr> </Table>

What is the song sound of silence about