Have you ever screamed with fright into your swim mask and snorkel? I have! It's quite a noise!
I was gliding along amongst the rooted aquatic plants, admiring their beautiful leaves infused with light. The stems were floating gracefully around me in a serene and calming manner. It was almost mesmerizing. But suddenly, a large (probably only about 9 inches long) painted turtle zipped up in front of me and out of the way. I wasn't expecting activity, or a sudden darting movement of this nature, and reacted instantly with a loud scream - I was the only one who heard it, enclosed within my snorkel and reverberating through my mask. The amplification of it made me more freaked out.
After recognizing what it was, and not feeling threatened or nervous, I could only laugh at myself. This is how I imagined it:
Hat tip to Edvard Munch