Remove the coarsest outside sticks of the celery and the green tops and save for another use. Cut the inner sticks thinly on the diagonal and place in a salad bowl. Add the garlic to the celery, then season with salt and the chilli flakes and mix well.
Prepare the squid. Rinse it well in cold water, then pull the tentacles, head, stomach and quill away from the body. Cut the tentacles a