Firstly, I should note that Picasso never explained any of the imagery in the painting. However, the bull is thought to represent either Fascism or Franco himself. Other symbolic images include the horse - which is thought to represent the suffering people of Guernica (dead and wounded); .
There are many other symbols.
Also note the flower held in the amputated hand - this flower is thought to symbolize regeneration and relate to a famous old oak tree in the town of Guernica under which Spanish kings of the past used to swear loyalty.
There is reference to this tree in the site below, but not the connection between the tree and this little flower - the only sign of life and hope in the Guernica painting.
