Why? Two reasons: taste and it feels good when they gnaw on the cable. They can be very precise with their gnawing too.
I see this behaviour in my vegie patch too. They will eat a whole tomato and then just bite dozens of others just enough for their incisors to "pop" through the skin and then not even finish biting through. One season they just like eating the freash plump beans, gnawing through the pod, spitting out the bits of the pod and eating the bean, and biting exactly where the bean is! The next season they left the freash beans alone and just out the dried out beans that I was saving up for seed for the next year!!!
Flaming little blighters!
Thanks Les for your suggestions too! Thers is little by way of foraging natives whete I live, and I do try to be careful with birds as there are lots of native birds around. I also need to consider my vegie patch and chooks too and secondary poisoning as you say. For us it's the vegie patch that attrats rodents. Not practical to close it off to keep them out.