Its probably food debris. Sometimes the food may sit in the socket for awhile and the bacteria digest it, leaving that debris/plaque-ish type of material. Keep the area clean. As long as it doesn't worsen, I would say its healing fine.
Thankyou I kindof thought that might have been what it was but wasnt sure
I had posted earlier about a root canal that I was due to have today, but was concerned my tooth was cracked. As it happened, when he removed the filling it became apparent that my tooth was actually split and so I had it taken out (my first and not too much fun).
I was told that if you swill or touch it, then the clot can fall out so you have to be really gentle for the first day. Maybe this is what happened. I think if this happens it may or not re-bleed, but if not I think that the lack of a clot may just make the socket a little sorer for a while.
I am no expert but I thought that I would give you my thoughts.