I got into shape because I took kick-boxing lessons every day to prepare for a fight scene with Taylor Lautner. I really wanted to lie down and eat Chinese food, but I kick-boxed every morning and ran. If someone was filming you with your kit off, you'd do the same thing.
Two or three notes of music can instantly make you feel sad or tense or afraid or angry. To do that in words is much more difficult.
I can't tell you how much we laughed on the set to have Alec Guinness in a scene with a big, furry dog that's flying a space ship.