If you notice that your pet has swallowed a harmful substance, take them to the vet immediately and give the vet as much information about the substance as you can. Take along a sample if possible, as the treatments for these poisons are often unique to one another.
Give your pet as much water as possible and if any of the harmful / poisonous substance is on their skin, wash it off with water.
Ensure all poisons are kept out of reach in your home if you have a pet.