Some half decent ideas, but not really thought through, so it doesn't really work as a wall/grid with only one valid solution. Zebra can swap to the grass group taking the place of either spear or blue, as both are also types of fish. The 'police' group is hugely vague, so blue could swap with copper, as that's also a kind of grass. Bill could move to the fish group, moving Zebra to the grass group and blue could then take Bill's place in the police group. I still solved it in forty seconds, but only because the group links leapt out atme and I made two lucky guesses early on, which left me with two groups that had only one pair of swappable answers.