Black rubber in clear PETG.

Hi everyone, I recently canceled a print halfway through after observing black particles in my clear PETG, at first I thought it was other material but it’s rubbery and flexible. It seems like maybe a o-ring, seal or other part. Anyone have any idea what it could be?

Hi everyone, I recently canceled a print halfway through after observing black particles in my clear PETG, at first I thought it was other material but it’s rubbery and flexible. It seems like maybe a o-ring, seal or other part. Anyone have any idea what it could be?