Even though Buck loves John Thornton, what also has a hold on his heart?

1) He would often seize Thornton's hand in his mouth and lay at his feet watching him
2) He would kneel down and roll over on his back and wait to be petted
3) He would bark loudly when Thornton left and then bark loudly when he returned
4) He would bring Thornton his slippers and his newspaper to read