The string is a really neat idea, but in practice it makes both characters unpleasant to control, because they're both weighed down by each other. I tried all levels and couldn't finish any of them (except 5 lol) because of some frustration with the physics.
The fact that the chatacters can't interact with things of their own color is very interesting, and I wish it was implemented into more of the puzzles.
I haven't encountered any puzzles that required the swap mechanic, so maybe that could have been expanded upon as well.
A minor problem I've noticed is that a lot of the puzzles required the rabbit to be on the left and the cat to be on the right. Given the control scheme, it would have been nicer for it to be the other way around to make it less confusing for solo players.
So in summary, this game has great ideas, and less than ideal execution in my opinion. Amazing job nonetheless!