OK, so we may have connected a dot or two extra in an effort to have a laugh at your expense. At least your panties aren't in a bunch (euphemism).
What you wrote was not exactly a known euphemism, but close enough to the phrase "spanking the monkey" that I leapt. That phrase is one of thousands of euphemisms for a particular form of self-pleasuring (not speaking of post-processing) that primates (including homo sapiens) are noted for practicing. If you were there with a school group, you were lucky that the ape didn't demonstrate it for you, as they are know of enjoying performance art, and school groups bring out the best in them. If he was not behind glass, he could just as likely hurled a feces or two at you, as captivity has a tendency to force gorillas into acquiring new hobbies.
Knowing that this shot was taken behind glass with a group of youthful competitors around you gives me greater appreciation for it. I was wondering about the foreground, but now assume that it is wood stamped concrete. Your shot does well to not emphasize it. What I like most about it is the graphite-like contrast of the dark tones. You stopped juuuuust short of the threshold of going too far with the post processing and hitting the blacks too hard, IMO. I think on a metallic paper, or even with Hahnemuhle's Photo Rag Satin (that develops a bronzy quality with carbon inks) it would be quite striking. There is a lot of personality that can be read into his countenance.
