It vibrates its tail - making a sound similar to that of the rattle-snake.
Yes. All snakes are predators.
Given the vague description - Either a Gopher snake or a King snake - neither of which are venomous.
Yes. There are 15 species of snakes in Oregon, including the gopher snake, rubber boa, kingsnake, garter snake, and western rattlesnake. The western rattler is the only venomous snake in the state.
The harmless milk snake mimics the colored banding of the venomous coral snake so predators will avoid it.
Gopher snakes produce a loud hissing noise with their glottis which can be intimidating to some animals. However, they also vibrate their tail and, if they are on dry leaves, the sound is almost the same as that produced by a rattlesnake's rattle. It is a form of mimicry that the snake uses to frighten off potential predators.
Its a warning to potential predators that the snake is venomous.
Belcher's Sea snake (Hydrophis belcheri) - is banded in light and dark stripes as a warning to potential predators - that the snake is venomous.
The milk snake is a prime example of mimicry. Many predators will recognize the colorful bands of a coral snake and leave it be to avoid its deadly bite. The non-venomous milk snake mimics the coral snake's banding, so predators will mistake it for a coral snake and not attack it.
They are not venomous.
The snake you're thinking of - is a Carpet python. It's a non-venomous species that grows to about 3 metres.
All snakes are non-poisonous but there are venomous snakes as well as snakes that are non-venomous. Rat snakes, gopher snakes, king snakes, garter snakes and boas and pythons are some examples of non-venomous snakes.
Some reptiles mimic venomous snakes - as an example, the (harmless) banded king snake has the same coloured bands as the coral (highly-venomous) snake. They're just arranged in a different order. Since both snakes live naturally in the same area - the banded king snake is avoided by most predators because of its resemblance to the coral snake.