...another keeps rubbing his hands together, another is biting his fingernails, still another grabs the arms of his chair tightly and one keeps running his fingers through his hair. (Para. 5)
keep (on) doing: continue to do
Whatever happens, keep (on) trying. 不管发生什么，坚持努力下去。
I don't know what's wrong with me today: I keep breaking things. 我不知道今天我怎么了，老是打破东西。
My parents kept encouraging me to study. 父母不断鼓励我学习。