Many were so alarmed by the accuracy of Daniel's prophecy. The leopard with wings was Greece and Alexander the Great rose and conquered the known earth within a very short period of time, however, he died young. After his death, the Hellenistic Empire was divided into different parts which was described as the northern, southern, etc. in Chapter 11. Some Jews who only read the Old Testament, have been reading Daniel for the prophecy of the end of days.
I have heard differently for the following terms :
Sea - Jews in the old days consider the sea as mysterious and things coming out from the sea would be "no good"
the Bear being able to stand on its feet like man and having a human heart - Nebuchadnezzar finally praised G-d (Daniel 4:34-37).
