It was sudden from Sango's side. The voice came out of nowhere along with the distortion of the space around them, bending into variable shape until it squeezed out the appearance of a being.
A being that Sango could only describe as a child at first glance. He knew better than to make the mistake of assuming the being to be the same age as his appearance dictates him to be.
By no means did Sango make the mistake of letting his guard down. All through, right from when he passed through the portal and got into the main base of the black tortoise guild, Sango has made it his concern to set up his perception at all times.
He had to be ready for anything, it did not matter where he was or who he was with. Never will he make the mistake of handing out a hundred percent of his trust to someone he has never once met with eye to eye.