Upon hearing this, I felt like nashing my teeth and pulling my hair. Zanshin, often translated as 'remaining energy' is one of the more important high level practices.
I have read about Zanshin being referred to as budo spell. It makes your art come to life.
Zanshin is a large and complicated word, but let us start with this one question to begin the exploration of Zanshin's ways...When does a technique end? At what moment may you begin to focus on something else other than your uke?
Most Aikido schools practice like this...uke attacks. Tori/nage does a technique. Suddenly there is a neutral time from when the impact from the fall happens to the set up for the next attack.
This is fine, but this is not the high level stuff. There is no magic in practicing like that. There is no focus that leads to those Zen states of mind.
In aikibudo we should strive to be aware of space and connection at all times.
When the uke sets up to attack, we become connected. He attacks, then is thrown. Now is when most people end the game - but really it is just beginning.
Most people practice like uke is slain upon impact to the ground. Many styles even pose in a deep kamae to look cool. The primary concern after is thrown is...is uke restrained or...is uke far away enough/in a difficult enough angle he cannot affect me after the throw.
When I practice with Aikido folks from different schools, I always throw them from the ground - by grabbing their legs and pushing. They seem very surprised like a whole new world opened up to them. Funny, Judo guys don't seem to have this problem.
So the rule has to be - while the throw is happening tori must be moving to a safe place. Once uke lands, they should be given permission to continue the attack if they feel like they can.
So now we assume, Tori threw uke and the correct distance was maintained. Is the technique over? I say no. You can be relaxed and calm, but keep the focus. Intently watch uke as he rises from the floor. The whole time correct distance and focus must be kept. Uke - as you rise from the floor keep focused on that guy who just threw you. Maybe he is showing a weakness as you rise - another window of attack.
This is part of Zanshin. This is the remaining energy. The focus remains sharp throughout the practice. At all times, uke remains dangerous. At all times tori remains focused. I promise you - train like this and it will transform your practice.
Here is an excellent zanshin article