The imagery of the thorn necklace digging into Frida's neck represents the constant pain she has had to endure in her life, particularly in her relationship with Diego.
The pet monkey on her left shoulder is known to be a gift from Diego her husband, symbolising Diego himself in the painting and the pain he has caused her.
The black cat over her right shoulder is a traditional symbol of bad luck, which could be reference to her divorce, or the bus crash she was in earlier in life.