How do animals tell the gender differences between humans?
For example: some dogs, cats, or birds, just prefer a specific gender to bond with.
Another example; when an animal is abused by, for instance, a male.. he fears them, and feels safer bonding with a female. I know this from owning a cat who had a history.
How do they know that human is a female or male? Is it the voice? Is there a smell? Do they just sense it?