It was quite rare for Theron to be taken off guard. But while he was caught unawares, he wasn't actually surprised.
This wasn't his territory, but instead that of another. If the tunnels had been perfectly curated to forge a formation of sound waves that amplified and dulled echoes, there was no reason for them to not be able to do it in reverse.
Theron could easily imagine a scenario where they had known the moment he entered and had been tracking his movements all the way.
Of course, that was also the worst-case scenario, and while he had taken it into account, he didn't feel that it was likely.
This was much more in line with what he thought might happen. They could detect him, but there were limits, or else, in all likelihood, it wouldn't have taken them this long.
And oddly enough… there wasn't nearly enough hostility given the situation.
Theron simply turned his head back to find a young boy maybe just a couple of months younger than him, if he was younger by much at all.