The video shows multiple failed attempts with various items. Only the spinach works to give the girl enough strength to hold the shark's mouth open. The solution is counter-intuitive and requires trying different objects until the correct one (spinach) is found.
The puzzle's solution relies on a humorous, non-realistic outcome (spinach granting super strength). If other items fail, consider unconventional solutions. The video explicitly states that the effect of the spinach only lasts for a while, implying a time-sensitive element, though the video shows the rescue happening immediately after.