Every now and then I have to think about something I read in Wikipedia:
People, and in fact most other mammals except members of the cat family, will typically accept food sweetened with sucrose even if they are not hungry
And that's so true. Often, even when my stomach is full, or when I have no appetite for, say, a piece of bread, my head thinks, "Ah, a piece of chocolate would really hit the spot just now." And that always seems to fit... thinking of eating, say, a potato makes me think, "Nah, I'm full, thanks mate," while thinking of eating a piece of chocolate makes me think, "Ooh, yes please."
Resulting occasionally in my eating far too much chocolate, biscuits, and other sweet junk food. (Hey, my BMI of about 27.5 didn't just set itself! *sigh* I need to lose weight.)