In Euthyphro, his father committed the crime of murder, and his claim was that it was just and that the murdered man had killed a slave. Euthyphro's response to this is that it doesn't matter because his father murdered and that is against the law. He said, "It's ridiculous that you should think it makes any difference whether the victim was a stranger or a relative, and not see that the sole consideration is whether or not the slaying was lawful . . . because the pollution is just the same." The way that Plato is making Euthyphro think is, for lack of a better term, an "ideal" frame of mind. To where unlawful acts will be prosecuted even if the defendant is one's own blood. This applies to the case in the fact that the Frenchman did an unlawful act, whether it was in France or Thailand. Thus he should be prosecuted for his unlawful act even though it was not committed in his country of origin.
Hume's moral sentiment theory is that everything is led by sentiment. Instead of using one's logic you would use your sentiment or emotion in making your decision to do things. An example of Hume's theory would be that if I were to give food to a starving person I did that because I wanted to feel good about myself and therefore I did something good for someone else. This applies to the case in the fact that he never used sentiment to think through his action. He didn't use his sentiment to think; he thought that what he did was good to him without thinking about what it would do to the girl.
Stevenson's emotivism theory is that the basis of all morality is that we are driven by emotion. Everything we do when forced to make decisions based on emotion or sentiment rather then logical. For example, if you see a train rolling down the tracks towards a group of five people, and a separate track that is connected with only one person and you have the lever placed in front of you, would you pull the lever and have it kill the one person or have it blow by and kill the five people? Each person may have a different answer but each person is answering based on what their emotions are telling them.