Some years ago I used to dive regularly in the Indian Ocean. It's an amazing thing to do and I recommend it to everyone. I saw many incredible things. One of the ones that sticks in my mind was this one Triggerfish that decided that it wanted me to leave it's territory and to emphasize it's point it decided to attack me! Despite our enormous size difference this thing would NOT back down and kept swimming at me then darting away at the last moment. I had time to take some ( very poor) photographs of this happening. I eventually retreated to a safe distance as he was probably protecting his young or something and I was starting to feel guilty that he was spending so much energy on trying to frighten me. I remember thinking at the time it would be amazing to be able to sketch this.
This drawing was done in 35 minutes flat using a sharpie marker and Photoshop. I'm trying to get quicker at this sort of stuff.