Rats! They ate my cables again!
The hypothesis that rats prefer to bite telephone and PVC wires is proven to be true.
A large percentage of fires in buildings in the USA are believed to be caused by rodents like rats, mice and squirrels. Because their teeth are constantly growing, rats need to chew constantly. When rats chew on power cables and expose the copper cores, they risk electrocution. The sparks emitted can ignite a fire if there are any flammable materials in the vicinity.
Would your results differ if this science fair project were to be repeated using different types of animals like mice or squirrels?
The science project can be repeated with different types of wires – eg Teflon coated wires.
How to stop rats from chewing house wiring - http://www.ehow.com/how_5712971_stop-rats-chewing-house-wiring.html
Rodents and fires - http://www.homeinspectionsbyjerrykellyiii.com/RodentsFires.html
Live electrical wires gnawed by rats can become exposed and cause short circuits or electrocution. Ensure that no flammable materials or gasses are within reach, and perform this experiment in a well ventilated laboratory under the care of a qualified adult. Disconnect ALL electrical connections before handling the cables. Ensure that protective gear (insulating gloves)/goggles are used. Rats should be handled with care as they bite!