The cartoon cat hits the cartoon dog over the head with a wooden plank and an angry lump rises from the top of its head. The dog’s face turns red and steam escapes its ears like a whistling kettle. The cartoon cat is frightened. He presses the lump back down with his finger but it returns the moment he lets go. The dog is furious. The kettle blows. The dog chases the cat around and around and around. Frantic music plays.  We teach our son the word ‘gentle’ by stroking the back of his hand over and over but he…