It is deffantly possible for her to cut her tongue when she licks the can. When I feed Karma tuna or any wet food for that matter I put the empty can into a plastic baggie before I put it in the trash. That way I know if she were to go looking for it she will most likely not smell it and hurt herself.
Next time you open a can run yor finger around the inside edge. You will notice that it hutrs and may cut your finger. Now imagine if that were your tounge. The above poster is right, you need to put the left over tuna in a bowl for your kitty.
Don't get discouraged, we all love our kitties and want to do whats best for them. It is our responsability to keep them safe.
I usually let mine eat a few tuna flakes out of my hand rather than give them the tin, I wouldn't want to take the risk - a cut tongue could have serious repurcussions for the cat's health if it is put off eating due to the pain of it for any length of time.
I don't want to scare you, but please watch your kitties tongue very carefully. When I was dating my hubby, he had a beautiful black cat named mischief. His dad gave her a tuna can to lick, and she cut her tongue, but we didn't know it at the time. To make a long story short, it became so infected that there was nothing that the vet could do for her. We ended up having to put her down, because the vet could not repair the damage to her tongue. He tried stitching it, but the tissue was so deteriorated that there was nothing to stitch. Sadly, we had to put her down because the vet said that cats can't drink without their tongues. It was a horrible experience. So please, watch your baby. The only reason that we knew that Mischief had cut her tongue was because she had terrible not "normal" breath. By then it was too late for her.