TF is this that I found in my salad?

[thoonerismspread]

I almost broke my tooth on it. Must've been in the bag of salad leaves that I'd bought from aldi.

Burnt crouton? Coal?

It could possibly be a burnt crouton but I don't think so? It's so hard that I can't crush it. There werent' any croutons present, was just a bag of leaves, of course that doesn't cut out cross contamination.
Coal-should I keep it for good luck?