dog story

A man walking his dogs gets caught in rain. The big dog refuses to move. The man gets sick and angrily kicks it out. Later, he wakes to find the big dog bringing him medicine, but it bites his needle. Next day, a coin toss decides who goes out. The big dog wins, but the man cheats and takes the little dog to the beach. Left alone, the big dog ruins the furniture. For their birthday, the big dog gets a bun, while the little dog gets a real cake and a huge party. The sad big dog just cries. Why???