【语法 理解】It would have been natural for him to go to sleep,but...It would have been natural for him to go to sleep,but when I looked up he was looking at the foot of the bed,looking evry strangely.It 是指代go to sleep吗?looking evry strangely 这里的looking是非谓语么?现在分词做伴随状?look It would have been natural for him to go to sleep这个怎么理解?

it形式主语，是的，是指代to go sleep. to go to sleep would have been natural for him. would have been是虚拟语气，他应该去睡觉但没有去睡。意思是如果是平时，他现在应该睡觉了。
可能looking very strange才对，因为看上去很奇怪，用形容词。是非谓语，现在分词做伴随状语。
这里look up没有特别意思，就是向上看，抬起头看。

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It would have been natural for him to go to sleep意思是：我很想让他自然入睡

是的,让他去睡觉本应该是很自然的事,这里是虚拟语气用法
looking evry strangely 这里是现在分词表伴随没错 looking at the foot of the bed,looking evry strangely

it 指的是go to sleep，这句话的意思是“他去睡觉本是很自然的事情”。
looking very strangely, 整个分句是伴随状语，修饰他“looking at the foot of the bed（看着床脚）”的状态。
look up 是往上看的意思