Mussels - how open is open.

I've got some mussels cooking. One is open just a millimeter. Is that open or closed?

a millimeter... no I would say don't risk it.

on one of the cooking shows the other day they were talking about how now the smell is what counts not whether they open

Hm... I wouldnt eat 1mm open one... i like to be able to get a finger in at least...

With mussels, if you can push them closed very lightly and they close and stay closed totally, then they are fine. You should be able to feel them close themselves, as opposed to just closing because you closed them...sounds odd but if you do it you will feel what I mean. They will often open and close if you bought fresh ones, depending on how they have been stored.
Open is open though so much more than a mm and I would bin it

ETA: are you meaning it is barely open after cooking? lol Sorry, I thought you meant before you cooked it ;).

I remembered now what they were saying some mussels have a very strong membrane that makes them opening hard, she said the ones that dont open when cooking try opeing them yoursefl you will know for the smell if they are good or bad