Animal psychologists believe most dogs are about as smart as a two-year-old human. Dogs can understand more than 150 words, count up to five, and notice simple errors such as one plus one equals three. 動物心理學家相信其實所有狗大概都有兩歲嬰兒的智慧。狗可以理解多於150個詞彙,數數到5以上,還能辨認簡單的錯誤像是一加一等於三。