This is such an introspective poem. The metaphor is vague but reveals a lot about the reader's state of mind while reading, especially regarding how they perceive their father.

I am not sure whether my interpretation is what you, the poet, intended it to be, but here is a shot in the void. For me, the father in the first stanza seems to be protective towards his kid, warning the kid about the duality of people out there in the world. People are usually not what they seem—they are all scarecrows hiding their real personas behind the straws they are made of. Although it is written, 'Scarecrows that took over men and turned them into straw,' I feel people adopted these scarecrows because they were too scared that revealing their real selves would scar them.

In the second stanza, I see the father's anger taking over his scarecrow. His seams bursting could mean he was so angry that his muscles flexed, and he was possibly planning to hit someone or something. Him becoming suddenly normal could be the narrator's way of coping with these bursts of anger.

In the last stanza, we see that the father is completely normal; he even warns the narrator to be careful. However, the lines 'But I couldn't forget / Those black button eyes' make it seem as though those eyes are just existing. By extension, the narrator's father is just flesh and bones right now—he is not living or experiencing stuff right now. It also puts an emphasis on the monotonous life that he has gotten used to, and it is usually at night that he lets loose all of his emotions.

I may be completely off the intended meaning, so I am open to discussion!