When you have two black Scottish Terriers that you, yourself have trouble telling apart at a quick glance, double is what you see. The two pups together are more obviously different. Gibbs is bigger, longer, and lower. He’s more “doggy” and Bonnie is more “bitchy” which is as it should be. Gibbs is stronger and more gracefully athletic. Bonnie is bouncy, cheerful, the happiest dog in this best of all possible worlds, the Candide of small dogs.
And then there are the swans and the geese. Both mate for life and you will rarely see one bird without the other nearby.