Board Thread:General Discussion/@comment-4504826-20160516034744/@comment-27620479-20160516082537

Well, my interpretation is that since Chara already had self-abusing and suicidal tendencies, they could simply overcome the auto-load that Frisk and Flowey can't. Frisk seems to value life, and enjoy making friends, since the only way to know their name is to spare and befriend everyone. Flowey also values his life to a certain point, because on the genocide route he begs Chara not to kill him.

Chara, on the other hand, eats buttercups, in a deadly dose, without knowing how much is that. In other words, they are showing as much as possible, in in their mouth, knowing that it will lead to a horrible death, while their mouth feels like burnng the whole time. You really have to supress your survival instinct for that.