We had a customer call us from Texas the other day. She said that the roofer had left the lead flashings foot exposed on the downslope of the roof and the squirrels had chewed this all the way up to the vent. This is fairly common. Roofers often leave the flashings foot on top of the shingles on the downside. Its supposedly makes a better seal, but I think its very unattractive and it lets squirrels gain access to the vent. If you have a roof done, I would recommend getting the flashing totally covered by shingles. Looks a lot better.