But you would need hearing exactly as keen as Miko's, if you wanted to hear the exquisitely careful footsteps of the Medium humanoid following them. Or, more likely, the whisper of her breath, and the slightly irregular beating of her heart.

Miko doesn't notice, at first. The sound of footfalls, of breathing, of a beating heart all blend in with the sounds of the group. And of the centipedes.

Eventually, though, she makes her Perception check.

A rogue, upon noticing that she's being followed, might privately hint to her companions that something's up without tipping off the pursuer.

Miko turns around.

"Who's there?"

Nobody!

(The footseps stop. The breathing stops. Unusually, so does the heart.)

"What?"

"Something's following us."

Whatever it is, it's good at hiding. Neat trick. If Miko went in for uncertainty, she might even suspect that she had simply imagined the sound.