Aster couldn't even react before he suddenly found himself enveloped in a dark enclosed space, while he felt as if a fierce predator was eyeing him.
Now, the previous would have freaked out a lot of people, but Aster wasn't one of them, in part because not only he knew the "predator" lurking in the shadows, but because he felt really comfortable right now.
As someone with a really strong soul energy, Aster's senses are quite sharp, part of the reason as to why he put a lot of thought into training parallel thinking, is because he needed it.
Because he receives a lot of information from his surroundings, so if he wouldn't have created secondary lines of thoughts, he would be overwhelmed by everything his senses transmit to him.