How bad is chocolate?

My cat managed to spill chocolate on the sofa. Emediatly removed the large pieces, but the tiny ones are difficult to remove and see on the black sofa. And freaking out, trying frantically to remove all traces of chocolate. How bad is it for them? Will a tiny tiny piece be really dangerous? (Cang seemore pieces but theyr noses and eyes are a lot better than mind).

The higher the cocoa percentage, the more dangerous the chocolate. So, a 70-80% dark/bittersweet chocolate would be a big deal and very worrying, a slightly lower cocoa chocolate (ie semisweet) would still be a big deal, though slightly less harmful, and a milk chocolate less of a big deal. White chocolate, though not good for cats, isn't actually poisonous to them at all.

If it were me, I'd vacuum the sofa to put my mind at rest.

When my cat was a baby I was eating a milkyway...she attacked me for it twice! I let her try a small piece, she ate it, and I told the vet. The vet cautioned me and I knew already...but she attacked me for it.  She was not interested in candy after that and nothing noticeable happened.