Check in and around the compost bins. Molds can harm animals, citrus peels are toxic to cats.
Look around the shed and garage. Antifreeze is deadly, a few teaspoons can kill a 20 pound dog. Old herbicides, pesticides, rodentecides should be properly disposed of.
Go to your garbage area, again, a lot of what humans dispose is dangerous to pets. Chocolate is toxic to dogs, grapes and raisins can be toxic to pets. If you thow away over-the-counter or prescription drugs, and your pet finds them in the garbage and eats them, they can be highly toxic.
Examine construction or work areas, flaked zinc, any iron product, flashing can cut, etc.
Check for past or present insecticides, Rodenticides etc.
Get close to your lawn. Any chemical fertilizer or weed killer or bug killer you use on your lawn gets walked in, played in and tracked into your home by your pet. Consider organics. Weed and Feed has 2-4D in it, and that has been linked to an increase in canine lymphoma.
Mushrooms in your lawn can be toxic to animals as well.