I know what this question entails so please try to keep it to experience and proven science.

I experienced a positive result with a Wireworld Starlight USB cable. I brought my laptop, DAC and headphones in to listen to some 2 channel speaker amps at a local A/V store. While listening to one amp for about an hour, the manager came in and asked me to try a USB cable and walked away. I was in the middle of a song so I finished it, replaced the cable and replayed it. I immediately heard a better presentation. I notice the micro details of a song. The way an instrument sounds, the reverb of a body of a cello, etc. I thought I could hear a heightened clarity, quicker dynamics in the song.

All I've read says you can't impact the digital signal with a cable but this certainly caught my immediate attention. Wireworld explains it's jitter reduction by geometry and separating power from signal as well as silver clad copper makes a difference.

Can a USB cable make an audible improvement to the analog signal? Am I experiencing placebo bias?

The equipment was static, including the volume. The only change was the cable between the laptop and DAC. Chain was Sony i3 core laptop playing foobar/ASIO flac & 24/96k vinyl rips into a Lynx Hilo DAC, balanced out to a Simaudio Moon 340i 2 channel amp into a pair of HE-6 headphones.