Throughout "The Scarlet Ibis", Brother demonstrates an extreme capactiy for cruelty to his younger brother. Perhaps the best example of his cruelty is the one that you mention, when Brother forces Doodle to touch what was meant to be his coffin. Brother's cruelty is, perhaps, driven by his anger and disappointment in his brother because he had hoped for a "whole" brother whom he could run, jump and play with, but he ended up with the fragile and sickly Doodle. Forcing him to touch the coffin is just another example of how Brother manipulates his fragile younger brother and basically punishes him for being the way that he is.
That's an interesting question. The story never really says why Brother is cruel to Doodle. We know that he is embarrassed by Doodle's inability to perform physically. We also know that his Brother's pride caused him to push Doodle beyond his limits.
But why this particular act of cruelty. It seems unlikely that it will encourage Doodle to work harder. Perhaps it will by making him determined to prove everyone wrong about his weaknesses. But the more likely reason for Brother's cruelty is simply that sometimes siblings are cruel. There is a German term, schadenfreude, that is used to describe the pleasure someone derives from the suffering of others. I'd say Brother got a little thrill at making Doodle suffer. Many brothers and sisters are mean to each other, and Brother is no exception. I don't believe, however, that he would ever mean to do Doodle any real harm, just scare him.
Take a look at the link below for more information on the themes of the story. The information on the theme of Brotherhood might prove helpful.
This question is the type of question i'd ask because i wanted to know why his brother to that to him but it never says it in the story.
I believe because doodle's brother was very cruel and mean to him.Doodle was frightened when his brother showed him the coffin and made doodle place his hand on it.