The three animals in the center circle represent the three basic human faults: hatred (snake), passion (rooster), and ignorance (pig).  According to Buddhists, these negative emotions underlie most of the problems humans create for themselves.  Each animal in the picture is connected with the other two, showing how each of these tendencies leads to and reinforces the others. 

The outer circle shows the effects of karma, both good and bad.  As shown on the right side, bad karma draws one down (note the rope that connects all the figures together and is drawing them down, though I can't clearly identify the actions there).  Good karma (such as giving and religious practice) lead one upward to enlightenment.