The thought bubbles are easy, for household members they rotate between your wishes lifetime wish and motives, If your hungry your think about food, if there is a vampire around your think about vampire if your a normal sim. NPC sims only have one wish and that is whatever rolls in the first window, but they do the same thing roll their motives and wishes and if they have a lifetime wish they roll that. Also if they are around sims or objects they may have a opinion on it, x means they don't find that object partially interesting or have low relationship with that sim. They sometimes roll their moodlets too, especial when you do something to change their motive status.