X and his wife went for shopping leaving behind their dog in their car which they had locked after pulling up the glasses of the windows. For reasons unknown, the dog probably got excited and broke the rear glass, probably with its paws and jumped out. A fragment of the broken glass flew at the face of one Y, a passerby, and pierced into his eye resulting in its loss. Y sued X for damages alleging negligence on the part of X. What defence can X take: