These spurs are connected to a venom gland located in their thighs. When the platypus is threatened, it can use its spurs to inject venom into the attacker.
It's important to note that only male platypuses have spurs and can inject venom, although the venom gland is present in both sexes. The venom itself is a complex mixture of proteins and is highly effective against other animals, but it's not usually fatal to humans. However, it can cause intense pain, swelling, and even temporary paralysis.