acrosome reaction...

'Let me in ...please let me in!'
The fastest of them banged his head on your wall,
How can you be so passive amidst such a din?

Your wall...
What should I it call?
A liquid filter kind
A filter is sure your mind!

You leave nothing unchecked
Even if he is wondrously decked...
Even if he is pleading, crying, wailing...
Even if his head got a swelling
By banging so continuous...
Your wall...so strong...hardly porous!

You and your wall
Keep the big and the small
Out of bounds till you're sure
You got him filtrated pure!

The process is a complex one
Often termed 'Acrosome reaction'
I find magic in it...
The way you select the breed!