Image on left is from 4 days ago, but the pimple was slowly forming over around 2 weeks.
The goop was sticky, not oily. Earphones are Panasonic RP-TCM130.
I was not able to find an explanation.
Something to increase cable lifespan, lubrication, rubber disintegrating, sweat and earwax that somehow got into the cable, dielectric grease, no clear answer.
At first I thought the wires just somehow twisted. Nope.
You gotta be careful with baby headphones. If it’s a boy, he’ll keep the cord. If it’s a girl, she’ll loose her cord, and her teeth will turn blue.