how do we explain what we want?

with reference to the two previous exercises

• saying what you want
• or showing what you want 

generally speaking,
people find it easier to explain what they want the horse to do
by physically doing it themselves,

(i.e. 'showing' is easier, and more accurate, than 'saying')

because

• it highlights whether you really understand what it is you are trying to achieve, and
• if you don't fully understand what you're asking for,
• it allows you to work through the movement until you do understand it

And then once you have it straight in your mind,

demonstrating it with your own body means

• anyone, regardless of age, breadth of vocabulary, and whether or not you have a common spoken language, can understand what it is you are looking to achieve

So now your body knows what you want him to do....