Caterpillar Question

This was on the ground by the front gate, and could possibly have dropped from the gum tree overhead. It was about 3cm long, and a bright green. I've checked online and it doesn't seem to be a goat moth caterpillar or a witchety grub (wrong colour). Whatever it becomes at the end of its cycle is likely to be large! Any ideas, anyone?
There is so much bracken on our property that often all you hear of animals and lizards is a thumping or skittering as they run away. I caught this guy napping. His head popped up and he stared at me as if stunned, then after a few long seconds, decided to make a run for it.
This particular walk was full of kookaburras - I think I heard several different choruses from at least a dozen different bird groups. I'm convinced that they warn everything that I'm coming!