DVD supports an absolute amazing amount of features many of which were rarely if ever used, and some never implemented on most players, likely.

It's why the original Matrix DVD dual layer release was so hard to duplicate / replicate by pirates/"enthusiasts" in a way that would fit on single layer DVDs. One of those was a secret "follow the white rabbit" mode that lead to hidden content.

doom9 had reams of guides dedicate to the matter: https://forum.doom9.org/showthread.php?p=313722