I can't believe that PVC is a food source for any mammal (maybe a few bacteria), so I'm not sure what the reason/motivation is. One often sees the nibbling close to where a cable passes through a hole (e.g. in a joist), in which case they might be trying to reduce the 'obstructions' so that they can get through the hole - but, as I said, that was not generally the case in the house I recently saw.
Whatever the reason for the nibbling, in that house one can but assume that the very dramatic discrimination (between T+E and 'everything else') was based on taste and/or smell - probably not colour, since they attacked white, grey, black and brown sheathed 'small cables', but very largely spared (both white and grey) T+E ... and not electromagnetic fields, since everything was switched off.
Kind Regards, John
