why a bird cannot eat the pork it is holding in the mouth

it is holding in the mouth
把it is删掉
hold改成被动

有问题，一个句子中不能出现两个谓语动词，你的句子中eat和is都是谓语动词，所以不对。可以把it is去掉，或者把it改成what。

Why cannot a bird eat the pork held in its mouth?

把it改为which或that，后面的就成为定语从句，应该就可以啦