Telling if small pieces of meat are cooked - blind or colour blind chef
Texture. Although I can see perfectly, I use texture to tell me if pasta is done, for example. It's obvious for spaghetti but I do it for macaroni too, or any shapes. Just stirring a pot full of boiling water with raw macaroni, then stirring a pot full of boiling water and cooked macaroni, is a very different experience. Stir frying raw meat, partly cooked meat, and cooked meat will also feel different. Grilling meat is definitely a time for everyone to use texture, probably some variant of the press-the-ball-of-your-thumb rule.

To a lesser extent, smell. This is what I rely on to evaluate baked and roasted things, long before I open the oven to look at them or touch them. It won't help you grill a steak though.

FYI, I asked Christine Ha on Twitter, and she replied 


  By feeling the texture of the meat… And also not being afraid to taste


Which is as close to "from the horse's mouth" as it seems we will get in this thread.