Rodent incisors grow continuously and have to be worn down. Electrical cable insulation happens to be almost exactly the right hardness for that job, which is why chewed wiring turns up in so many squirrel and rat attics.
What the damage looks like
Insulation stripped in short sections, often at a point where cable crosses a rafter or joist, because that is where an animal can brace against it.
Bare copper visible, sometimes with fine tooth marks along it. Occasionally a section of cable chewed entirely through, which usually presents as a dead circuit.
The dangerous version is partial: enough insulation gone to allow arcing against framing or against the neutral, but not enough to trip a standard breaker.
Why it does not always trip a breaker
A standard breaker protects against overload and dead shorts. An arcing fault can draw well under the breaker's rating while still producing enough heat to ignite dust, insulation or dry timber.
Arc fault breakers do detect this signature, which is one reason they have become standard in newer construction. Older attics frequently have neither.
What to do after a removal
Have the attic wiring inspected before the insulation goes back down. Once new insulation is blown in, damaged cable is invisible and stays invisible.
Photograph anything found. It matters for insurance, and for proving the sequence if a claim is made later.
Repairs are an electrician's job, not a wildlife company's. Any company that offers to splice your attic wiring should be declined politely.
Reducing the risk in future
Exclusion is the real answer. Nothing in the attic means nothing chewing in the attic.
Where cable runs are exposed and accessible, conduit or protective sleeving at rafter crossings is cheap insurance during a restoration.
Trim limbs that give roof access. Squirrels reach most attics from a branch or a utility line rather than by climbing a wall.