If in Australia, and you hear the shout:

TIGER!! TIGER!!

The Tiger's Stripes

The Eastern, or Common, Tiger Snake (Notechis scutatus) is typically banded or striped dark brown above, with a yellow to olive belly. Their habitat is much of the south-eastern mainland of Australia, while a sub-species also makes Tasmania its home. They frequent inland waterways and billabongs, like the lower lakes of the Murray River, and don't mind either a swim or even climbing a tree to snack on a bird's egg or baby bird. Their usual diet consists of frogs, lizards and the occasional fish, while they have sometimes been known to feed on carrion such as roadkill. The adult can grow up to 1½ metres (5 feet) in length and they are unusually territorial and aggressive for a snake, attacking with remarkable speed if disturbed or threatened:

I was swimming at a mate's dam once. There was a group of us, we were all a bit drunk and mucking about on this raft that we'd built. I dived into the water from the raft and broke surface to everyone shouting at me. A Tiger was making its way towards me from the bank! Needless to say I got back on the raft sharpish!
- An h2g2 Researcher's first-hand experience of a Tiger Snake.

Burning Bright

Tiger Snake venom is highly toxic, and the creature produces it in excessive amounts. So much so, you can milk them like a cow for days on end. For venom that is, not milk¹. Tiger Snake venom is mainly neurotoxic, so it affects the central nervous system, but also causes muscle damage and disrupts blood clotting. An elderly woman was bitten while she pruned ivy on her fence in Kew (an inner suburb of Melbourne) in 2003, and she was dead within seconds. There is an anti-venom available, but if you are unlucky enough to get bitten by a Tiger Snake, you'd best be nigh-on next door to a hospital as fatalities from Tiger Snake bites are second only to the Brown Snake in Australia.