But animal children grow up and stop playing to a certain extent as age advances, precisely as human children do. Each settles down into a more practical condition of life. They dislike to have thier games and play disturbed, and if the mother dog growls because her playful son has continuously tumbled over her while she was sleeping or the cat mother slaps her kitten because he plays with her tail ㅡ it is a display of the same kind of emotion that prompts a human mother to rebuke her child in the nursery for making too much noise, or for throwing toys out of the window.
Animals like ourselves feel every sensation of joy happiness surprise disappointment love hope ambition and through their youthful games an entire index of their future lives may be obtained
ㅡ The Human Side of Animals, by Royal Dixon.
I want to explore the meaning of the whole quotation in bold. (I find it hard to understand it:()
Any help would be appreciated. Thank you very much.