A surgeon leaving a sponge inside someone's body when they sew the patient up.
It could be, but it might be simple negligence instead. How?
I would argue that the sponge left in is not a case of res ipsa loquitur...but is just professional malpractice because in the case of the physician, we can probably determine what happened, proving negligence. Res Ipsa Loquitur, I believe, is used when we can't really determined what happened...but we know that something negligent must have happened. "Sir, I don't know what you did, but it must have been negligent."
With the doctor, an expert could be brought in to determine, with a reasonable degree of certainty, what happened, even if we never find out exactly what did happen.
The distinction, therefore, is in the difference between cases where we can determine what happened...and those where we cannot, but know that what DID happend does not normally happen "but for" negligence.
Otherwise, we could call many types of neglience...res ipsa loquitur...that normally would not be called so.