Ren asked Kestrel to stay here for a bit.
He took out a small spray can. There was just a dribble left in it. He spritzed that small amount onto his fingers and rubbed it around the spot where Kestrel was seated.
"It's a mimicry spray," he explained. "It's not very powerful, but it can give us a little extra time if we're hidden behind a door."
The mimicry spray could mask the smells unique to humans, making it harder for mutants to spot any nearby people. Its effect didn't last long, and there was a high chance of being discovered. Plus, it was very costly.
Apparently, Ren had just used this spray and a peculiar fish bone to sneak in undetected.
Once he was done, he cast a glance at Kestrel, opened the door, and quietly stepped out.
In the hallway outside, the metal-head guards strolling by didn't bother searching this storage room.