The music note «D» as i see it. Erythrocytes in the air.
I made it with Antonio Brech‘s soft : SIGCA.
Here is his website : https://antoniobrech.org/
You can Download the soft here : http://sigca.org/index.php/software-SIGCA
The FB group : https://www.facebook.com/groups/e.meta/
&Here you have the video, about how you use it :