Which of the following describes a failure to extract in a shotgun?

A failure to extract in a shotgun occurs when the spent shell casing does not leave the chamber after firing, which directly corresponds to the situation described in the correct answer. This malfunction can happen due to various reasons, such as a lack of lubrication, a dirty chamber, or issues with the extraction mechanism itself. When the shell remains in the chamber, it prevents the shotgun from loading a new round, interrupting the shooting cycle and necessitating immediate attention to correct the problem.

The other options illustrate different issues that could affect a shotgun but do not specifically relate to the extraction process. A shell being too large refers to a firearm being chambered for a different gauge or size shell, which is not a failure to extract. Having an unloaded magazine indicates that there are no shells available to fire but does not involve the mechanics of extraction. Lastly, if the fore-end does not cycle, it might suggest a problem with the action or cycling mechanism, which is separate from the extraction of a fired shell casing. Understanding these distinctions is crucial to diagnosing and addressing firearm malfunctions effectively.