Conkers are the seeds of the horse chestnut tree and are mildly poisonous to humans and most other animals. Eating a conker is unlikely to be fatal, but it may make you ill. However, deer and wild boar can safely eat conkers. Squirrels and other small animals, such as dormice, can also eat conkers, but they chew off the hard outer casing to get at the seed inside. Dogs should not eat conkers as they contain a chemical component called aesculin, which is toxic to them. In summary, while some animals can eat conkers, humans and dogs should avoid eating them.