My daughter cut her finger on a gl jar in Morrisons. Do people take legal action for things like this?

Today we were in morrisons, and my 13 year old daughter picked up a jar of gherkins. She didn't know, but the jar had a small sharp triangular piece of gl sticking out of it, and it cut her thumb. The cut is around 1cm long. It was bleeding quite a bit. I took her to customer services, with the jar as proof. The man there called the manager, and he saw the jar with the piece of gl sticking out. They called the first aider, who cleaned the cut and put a bandage on. The jar wasnt cracked or anything... it must have been a manufacturing error or something. What can I do about this? The manager said they will investigate, and maybe the next time we are there, he might give her a free dvd or something... but I dont think thats enough. Any lawyers seen anything like this? What can I do about it?