Sarutobi Hiruzen pondered this, then asked,
"So Toad Oil can strengthen my ability to sense Natural Energy?"
Fukasaku nodded,
"That's right. Without Toad Oil, you humans are different from us Summoning Animals."
"You can't sense the existence of Natural Energy."
Sarutobi Hiruzen immediately asked,
"I've heard that the other Summoning Animal sacred lands have their own methods of training in Senjutsu, besides Mount Myoboku."
"Are they the same as Mount Myoboku's?"
Fukasaku frowned at this. He clearly didn't want to bring up the other Summoning Animal sacred lands,
but he explained anyway,
"They're different, but the principles are similar."
"They all use specific substances from our bodies to strengthen your ability to sense it."
"Otherwise, you wouldn't even be able to sense Natural Energy in the first place. How could you move on to the later steps?"
"As far as I know, Ryūchi Cave uses venom, while Shikkotsu Forest uses something similar."
Sarutobi Hiruzen seemed to understand,
To train in an unorthodox Sage Mode, humans had to rely on bodily fluids from another species.
And it was precisely because they relied on another species' bodily fluids that the Sage Modes they learned differed, even bearing traces of that species.
Orochimaru's Kabuto was the same, but he went even further.
To stabilize his Sage Mode, he directly implanted cells from another species into his body.
That must be why humans can't truly make use of Natural Energy...
Sarutobi Hiruzen thought,
In essence, humans train in Sage Mode by using another species' methods as a foundation—a shortcut.
They can only use Sage Mode for a short time
and can't truly use Natural Energy to elevate their status and level of life the way other species can...
*Otherwise, there's no reason these short-lived species can live for a thousand years, while people who