This needs analysing. Any offers?
This seems to be about the guilt of the spanker. His perception of the world around him, as represented by the window he gazes out of (in to?) is an untarnished and unspanken buttock. Meanwhile, he’s spanking the figure on his lap, leaving a mark on its butt and his hand is blood red. The flowers, arguably the only beautiful thing in the room aside from the butts, are falling away from him. He feels his focus on butts, on sexual beauty, is destroying this purer beauty that his focus has been drawn from. And directly behind him (and out of sight from him, out of the light cast from overhead), peeking in on him is this elephantine rat. This is the clearest symbol of an issue (as rats are generally seen as that) that has grown altogether too large and remains unnoticed, at least consciously, because of the character’s focus on the great butt in the window.
Imagine the room as the spanker’s mind. We see a character who is blind to the world and himself, both. He looks away from whatever harm he is doing this sexual aspect of himself - the nude, prostrate and bespanked thing on his lap - and the harm that is befalling the beauty in him (the falling flowers), to focus on a world he sees as overbearingly sexual. Its butt is actually coming in through the window, blocking out anything else he might see. Meanwhile the pest in his brain - his problems, his demons or whatever lurk out of sight and grow disproportionately large.
His head, though… I have no idea about his head.