The strike of the Ouroboros Serpent was so sudden, despite the evasion from Rhion, it was already too late. He managed to disassemble himself, but the Ouroboros Serpent had already drawn him into its stomach, it was a testament to the power of Rhion the Ascendant Explorer that he was able to appear on the tongue of the serpent after vanishing from its stomach. However, that action stripped him of a greater portion of his power.
This also led to his slow and torturous death, because the Ouroboros Serpent had been a bit curious about how Rhion had been able to survive and escape from its stomach, even if this shell was its avatar, it was still something that should not have happened.
The serpent delayed consuming Rhion and it watched the Ascendant Explorer struggle to his death with disappointment. It did not bother trying to eat Rhion quickly, its interest in the Ascendant already faded.