What's up with these rivets?

[u/BoggleBadger]

Hey all! This is my first commercial flight since going to A&P school. I couldn't stop staring at these trails behind the rivets on the inboard leading edge of the wing. In the clouds they were a bit subtle, but they became really obvious when we broke through cloud cover and the sun hit them. Are these smoking rivets or just dirt from rivets that aren't flush? Would this be cause for concern?

[u/Jeanko1993]

Frettring corrosion 🫱🏽‍🫲🏼