These often depict your basic spinal and lower brain reactions, such as fight or flight, reproduction, attraction or repulsion, sex drive, need for food and reaction to pain. This includes the fundamental evolutionary ability to change and the urge to survive – all very powerful and ancient processes. Your relationship with the reptile in your dreams depicts your relatedness to such forces in you, and how you deal with the impulses from the ancient part of your brain.
Modern humans face the difficulty of developing an independent identity and yet keeping a working relationship with the primitive or fundamental parts of their nature, thus maturing and bringing the primitive into an efficiently functioning connection with the present social world. The survival urge at base might be kill or run, but it can be transformed into the ambition that helps an opera singer meet difficulties in career.