The way allergy shots work is they mix up a special cocktail of the things you are allergic to and inject you with this allergen soup in increasingly powerful doses to train your immune system to respond appropriately.
My natural reaction to getting a shot is to tense my arm muscles. It's not a conscious tensing...it "just happens" at the approach of a sharp needle. Of course when you tense, the shot hurts a lot more. By about the 3rd week of 3 shots per week I could consciously de-tense my arm and barely feel the shot.
Most of the real work was going on internally. There was no conscious activity, but my body was working hard to develop an ability to handle the allergens. My warm skin and sleepy disposition were the indicators that things were proceeding as expected.
So how does the tie to Zen?
If you are like me we bump through life in a semi-conscious fashion. Then an issue pops on the scene. Maybe I have an argument with a friend or co-worker; or, I get in a wreck; or, I lose my job; or my partner leaves me..."the needle". I tense emotionally. I tense physically. But that's not the end of it.
The real activity goes on internally as I mentally churn about how "I'm right" and "their wrong"...and I churn and I churn.
Like the needle, I can practice "de-tensing" when issues arise. This practice starts by recognizing the reason I tense is because I'm not willing to accept the situation. The world is one way. I want it a different way. I tense. I have separated myself and reality in the present moment.
Then the churning starts as my ego's defense mechanisms kick into gear. When I'm paying attention the next part of my practice also turns on...continually bringing awareness to the thoughts of anger and frustration...labeling these thoughts as "just thoughts"...just my thoughts...not something that is real to rest of the world. Eventually awareness dissipates the waves of ego emotion. The separation collapses on itself. I smile again...and the more I practice the more I'm able to handle the allergens of life.
Namaste and Friendly Bows _/|\_
(I also published this entry in my Sangha's blog located here: http://corvalliszencircle.com/2014/06/30/zen-is-like-allergy-shots/ )