The only mammal that lays eggs and is poisonous is the platypus.
The platypus is the only mammal which lays eggs and is also poisonous and venomous.
Male platypuses have a spur on their hind legs and they use the spur on their hind legs to inject venom into potential predators and rivals.
A platypus is a semiaquatic, egg laying mammal endemic to eastern Australia, including Tasmania.
The platypus is also sometimes referred to as the duck billed platypus.
The platypus lives up to 17 years although some may die sooner out in the wild.
Male platypuses are venomous and have sharp spurs on their hind legs in which they use to deliver a venomous injection, primarily during their breeding season.
Although the venom of a platypus is not fatal to humans, the venom still can cause pain and result in long lasting effects like swelling and even muscle wasting in humans.
Platypuses are generally not aggressive to or towards human, although the male platypus could inject you with venom if they feel threatened or are provoked.
It's best to observe any platypuses from a safe distance and avoid handling of them.