Riley says " the cat did it"
Ok seriously, hhmmm let me pull out my teenage mentality for a moment.......
-You have no idea how it got there and you were walking Riley so it couldnt have been hin
- you fell and used the chair as support and you had "object of choice" in hand and it scratched it
- the rivet on your jeans did it
- its always been there, didnt he notice before?