There is one minor flaw in your logic, that being the eel could simply sieze it from the top or bottom, with the narrow side fitting in quite easily.
You know what?
Sometimes the best thing I can possibly be is wrong, and whenever a scenario that just plain shouldn't work does I think it's completely awesome.
I also know it really sucks when they convince you that ,by george, they're gonna be OK and OOOOOOOOoppps.
With anything alive there's always the chance they're going to go against type, and for whatever it's worth, I'd be tickled pink to see them get along until they both die of old age.
In group settings I tend to feed heavier than is recommended as there's no doubt in my mind that full tummies go a long ways towards tolerance, if not friendship.
While feeding too heavily can cause obesity, fat deposits and a shortened lifespan, I'm fairly sure that there has to be a happy medium in there somewhere, with captivity itself not being something that our charges are genetically designed for and there's probably being no such thing as a happy ending.
For now, give it your best shot and enjoy the pieces of mother nature that you have custody of and maybe they'll just do the same thing.
I've been fascinated by animlas of all types my whole life and the longer I live the more I wonder if a lot of these dumb animals may not just be a whole lot smarter than we give them credit for, with some instances I've seen literally just live and let live, while by all right and reason it shouldn't be that way.
You have to admit, those are all beautiful, impressive animals, eh?
