The bait power's usage of the number 4 is a reference to superstition held in some Asian countries, such as China and Japan, about the mentioned number, due to it being a homonym for "death".
If the player attempts to summon The Old Duke using a multi-lined hook, such as the Early Bloom Rod, it will lead to multiple Old Dukes spawning in at once.
This is an homage to an oversight in Vanilla Terraria, where multiple Duke Fishrons can be summoned using a fishing exploit.
Similarly to the Truffle Worm, the Fisherman's Pocket Guide (and its combined accessories) will display a player's fishing power simply as "Warning!", due to the fact that The Old Duke will spawn when using this as bait in the Sulphurous Sea biome and no fish will be caught when not in the Sulphurous Sea biome.
In real-world bodies of water, the presence of bloodworms is an indicator of pollution, therefore it makes sense for this kind of creature to be present in the Sulphurous Sea, which is highly acidic and polluted.
Previously, the item's bait power was 69420%, as 69 and 420 are both numbers which are used in memes.