I came across this sentence while I was studying: 人間は話すことのできる唯一の動物だ。
I understand the meaning of the whole sentence, but I don't know why both 〜こと and 〜の are present. From my understanding, both have the ability to convert the plain form of a verb to a noun (ie. 遊ぶのが好き、遊ぶことが好き).
Is there another usage of the particle の that I'm missing here?
