The Australian Reptile Park celebrated the milestone for Elvis, one of its best-known residents. For those who don't know, Elvis is a saltwater crocodile. The park bills him as "perhaps the world's most famous reptile".

So what do you get for a prehistoric killing machine more than four metres long and weighing half a tonne? Apparently it's all about the meat.

Elvis chowed down on a cow's leg, charging keepers to claim his prize and throw it into a death roll. He should really act his age - that behaviour is more suited to a children's birthday party when the cake arrives. It's not the first time aggression has got the better of the big guy, either; he tore into a lawn mower in 2011, catching some attention and leaving his keeper a little concerned about the state of the yard.

"It's not easy playing tug-of-war with a huge living dinosaur like Elvis," head of reptiles Daniel Rumsey said. "I always feel the burn in my arms in the days to follow, and this time he felt stronger than ever.

"He thinks that he just grabbed a large prey item, dragged it in the water and drowned it then ripped off a piece. This is a natural behaviour that we see in wild crocs and it's awesome to see Elvis mimic this behaviour and showcase these incredible instincts."

Many happy returns, Elvis.

Sticking with reptiles, new research has revealed a previously unknown method used by certain snakes to avoid being killed by their own venom.

It works in a manner similar to the way two sides of a magnet repel each other, Associate Professor Bryan Fry from The University of Queensland says.

Snake neurotoxins have evolved to have positively charged amino acids on their surface, which bind to negatively charged sites on a receptor on animal cells.

However some snakes have evolved to replace a negatively charged amino acid on their receptor with a positively charged one, meaning the neurotoxin is repelled just like when the same side of two magnets are facing each other.

"What we've discovered is a really cool form of mutation where instead of that binding site on the nerve being negatively charged, some prey lineages like the Burmese python, which is a very slow moving terrestrial snake living where there are a lot of snake-eating cobras, have evolved the nerve pocket to be positively charged," Associate Professor Fry said.

"This is like trying to force two magnets together with the same charge, it's not going to happen."

Researchers have understood that certain animals, such as the mongoose, are resistant to snake venom through a cell mutation that blocks neurotoxins, but this is the first time the magnet-like effect has been observed.