Why does Edward Elric throw up after digging up his mother's corpse?

Question

In season 2 episode 7 of Fullmetal Alchemist: Brotherhood, as Pinako and Edward went to the brothers' old house to dig up Edward's mother's corpse to see if it was actually her they transmuted, it starts to rain. In a particular scene, Ed throws up a yellow liquid which I guess was a nicer way to depict vomiting.

But why does he throw up?

Answer 1

As you point out in the question, they are digging up Ed's mother, which is traumatic in itself. Additionally, Ed is a child and they are doing this for a traumatic reason: to check whether the transmutation that took his arm and leg and his brother's body was actually of her. Vomiting is a result of the stress response which can come from things like anxiety and trauma. Hence Ed vomiting from digging up his mother.