Some might think that a pony without much to say doesn't have a lot going on in their minds. Those ponies would be wrong. In fact, it's usually the quiet ones that think the most.
Marble Pie thinks a lot. Most of the time, she thinks about rocks, and how scary everything else is.
Big MacIntosh thinks a lot. Most of the time, he thinks about apples, and how complicated everything else is.
Now, throughout the good times and the bad times of Hearth's Warming, they think about each other.