Everything!
This comes from the ancient practice of observance of nature. You can watch the behavior of some animals to tell practical info, like when a storm is coming or how close land is.
Historically, the ancient Greeks, Romans, and Etruscans looked to animals and nature herself for divinatory clues. The Etruscans would actually look at the animal's entrails, and had a written system of divining from these pieces. the Romans would wach to see in which quadrant of the Forum lightning would strike to determine portents.
I also look to nature for divinatory clues. I feel that you can tell when you are being 'shown' and animal sign, and just seeing an animal. Here's how--if you feel drawn to look at an animal, or you are already looking in the space where the animal appears, then its a sign As for reading the signs, this takes practice, and study of many animal representations (for my divinitory animal signs, I use a blend of nDn animal lore, blended with that of the animal representations for my own spiritual path). Other things influence the sign, like speed or direction of movement, determination (ie determined or wandering) of the animal, number, gender, location, and color of the animal. Also, look for some cosmetic strangeness or markings on the animal, it may be a clue.
I thinnk domestic animals can also give signs, but we are often too close to pets to d-termine it sometimes. Livestock are also good divinatory tools.
I've seen no less than three animal signs in the last 5 days, and they seem to come in threes. One sign was meant for another (and received

), but I was privy to the event as well.
Keith