By now I hope you'll all have your heads around the idea of a mammal that lays eggs. This arrangement is called a monotreme ( one treme ).
There are only two monotremes on the planet, so there's no need for "I'm never going to remember all this !"
One is the Platypus ; the other, the Echidna.
The Platypus has fur ; the Echidna has spikes.
Both lay eggs, which sets them apart from other mammals.
The Platypus grows to about 64 feet in length, and eats cars with people inside them. The Echidna on the other hand grows to about 18 inches, eats ants, and is a shy nocturnal affair that rolls itself into a ball at the slightest provocation.
The difference in size alone makes it easy to distinguish between the two. My mate Bruce once shot a Tourist Bus, thinking it was a Platypus, and then his vacuum cleaner, thinking it was an Echidna, even though it hadn't eaten any ants, but Bruce is insane.
If there's anything else you need to know before travelling Downunder, give me a bell.
pics : platypus2.com.au.
echidna : abc.net.au