"But not even her happiness could chase the sadness from Prosper's face. They had all tried in their own way: Riccio with his jokes, Mosca by showing Prosper all the strange things hidden behind the dark doors in Ida's house. Nothing helped: Not even Ida's candy nor Victor's reassurances that he would think of something to help Bo. Because if Bo wasn't there, Prosper missed him like a lost arm or leg". p. 246 par. 3.
This paragraph really makes you understand how sad Prosper is without his brother Bo. Everyone tries to make him feel better but nothing works. I can relate to this part because I always am the one person trying to make someone feel better when they are sad. I hate to see people upset or in a bad mood so I will always try to do something stupid or funny just to get a smile out of them.
The last sentence also really touched me because I have a younger brother that means the world to me. By just reading the sentence, anyone can relate to the simile about "missed him like a lost arm or leg" because we can just imagine what it would be like to not have an arm or a leg. But this sentence is really saying that missing a brother is like missing apart of you. There is an indescribable relationship between siblings and I think the sentence really explains it. So I agree with Prosper, missing a brother is like missing a huge part of you.