Don't Look Back (The Phone Call by the Sea) 2

After a few seconds, his mother said to Xiaoming in an unprecedented, extremely terrified and trembling voice: "Son… listen to your mother, walk forward slowly right now, and absolutely, absolutely do not look back. Because… they know you found them." If Xiaoming was already facing away from them, how did his mother know that couple was staring at him? Unless… the couple had already silently stuck themselves right behind Xiaoming, facing the screen of his phone directly...