Left metal pliers in already slightly rusty vinegar for months, what is this cool reaction?

Hi! I was like 'well, i have cleaned the chassis, now it's still a workin vinegar, I should save it, oh, and let's clean pliers, too'. And forgot about the last part.

Now I found a cool foamy thing in place of pliers, and I understand that this is acid corroding metal, but I would like to understand what it the reaction and what is that iron foam and can I touch it?