Hi no Kuni was a land of striking scenic beauty and the forest surrounding Konohagakure no Sato was remarkable even by those standards. The dense forest hid lovely gems: rugged peaks, snow-fed lakes so clear you could see all the way to the golden sand at the bottom even in the middle of the lake and so cold swimming in those would have been night suicidal, turbulent rivers, rocky gorges and even small waterfalls. No one ever got to see this except the ninja since it was an area under Konoha military law, trespassing disallowed, regularly patrolled and just generally forbidden. All that regular travellers ever saw of Konoha Forest were the winding, confusing roads where the courier nin firmly escorted them, making sure no one took unauthorized side trips.
Of course there were areas that were forbidden for entirely different reason, the closest to Konoha being Forty-fourth Training Ground, also called Forbidden Forest. (Just because someone is a kick-ass shinobi who makes his own hidden village doesn't mean they are good at naming things.) From the outside those areas looked like your typical, run-of-the-mill forest, the insides were an entirely different story. In those places the forest was so thick that even in high noon it wasn't hard to find places completely surrounded by darkness. Those spots were inhabited by giant, venomous centipedes with ugly, pinkish-red, blotted bodies, giant, venomous snakes and pretty much giant, venomous everything. Naruto and his ANBU comrades were now running over one of those pretty, snowy cold lakes. They were running quickly, thanks to Naruto keeping break-neck pace. He wasn't one of those temperature-is-a-matter-of-discipline type of shinobi, he was only wearing his military issue sandals and the surface of the lake was freezing.
Since it was also one of those dangerous spots there were venomous, giant leeches that would chase them and try to both suck them dry and poison them. That was the other reason they were running.
"If my toes turn black and fall off its all your fault," he grumbled to his comrades who had all summarily refused to walk around the lake since that would have been taking an unnecessary detour and the Root didn't take those. The Root had great discipline and very cold feet. "And damn those overachievers!" But that wasn't directed at Sai, Tomiko-chan and Fū-san, but at the leeches who made yet another attack, making the water break in the sun. Naruto dodged and distracted them with a Kage Bunshin.
"What's the difference between poisonous and venomous anyway? Why are there two words for the same thing?" he asked, not from anyone particular.
"If it bites you it's venomous, if you bite it it's poisonous," Sai was the one to answer. And they reached the shore and a part of the forest that at least looked like it hosted nothing more dangerous than some boars.