DISCLAIMER: This is my understanding of how the mod works, not the actual mod author explanations. Maybe RD5000 can correct these, IF he wishes people to know the actual mechanics of his mod.
IMO, my previous actual lack of understanding lead me to roleplay an actual study of zombies behaviour with my friends, so it's up to you if you wanna keep reading this.

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Sandbox_HordesEnabled = "Are Hordes Enabled",
Sandbox_HordesEnabled_tooltip = "When disabled, zombies will only eat corpses if they happen to wander nearby and see it",

This settings is a feature that works similar as an """sound""" ingame. When a large amount of bodies are next to each other, they start sending signals that attract zombies to the body pile location, therefore, generating hordes. When disabled, bodies will not generate signals to attract zombies from afar, but will eat when roaming and find bodies in their line of sight.

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Sandbox_SpookyScarySkeletons = "Spooky Scary Skeletons",
Sandbox_SpookyScarySkeletons_tooltip = "Sends shivers down your spine, while they rip it out of you (Warning - stupid, funny, hard)",

No idea what that actually means, but I can edit this when RD5000 has a better explanation.

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Sandbox_MaxTimeToEatBody = "Max Minutes to Eat a Body",
Sandbox_MaxTimeToEatBody_tooltip = "The amount of in game minutes it takes for a lone zombie to eat a corpse",

If this setting is set to default (720), a single zombie alone will take 720 minutes (12 hours) to eat a entire body. If more zombies eats the same body, it takes less time (on default, 2 zombies take 360 minutes (6 hours).

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Sandbox_CorpseDrawWeight = "Horde Draw Radius Per Corpse",
Sandbox_CorpseDrawWeight_tooltip = "Amount of nearby corpses * THIS VALUE = the radius of the world sound when a horde event triggers",

This settings changes HOW FAR a SINGLE body attracts the zombies, if the HORDE settings is ON (if it's OFF, this can be ignored). This value stacks, so the more zombies is next to each other, the farther they attract zombies.
Example: Value is set to 20, so if I have 10 bodies next to each other:
10 * 20 = 200 -- Mod send signals to attract zombies in 200 meters range to that body pile.

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Sandbox_MinHordeDrawWeight = "Minimum Horde Event Radius",
Sandbox_MinHordeDrawWeight_tooltip = "A body pile must have a horde weight of at least this value in order for a horde event to trigger (minimum is Java side, can't go lower)",

If a body pile DOES NOT reach AT LEAST the value you set here, it will NOT send signals to attract the zombies. If you set the previous settings to 20, and this setting to 100, it will need AT LEAST 5 bodies to reach 100 and be allowed to send signals to attract zombies. For example, If you change it to 200 while keeping the previous settings to 20, it will now need 10 bodies to start attract zombies.
Remember that these values not only is a THRESHOLD, but is also the DISTANCE that it attract zombies. As well, if the horde settings is OFF, this can be ignored.

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Sandbox_MinHordeDrawWaitTime = "Minimum Time Body Exists Before Horde",
Sandbox_MinHordeDrawWaitTime_tooltip = "Once a body has been on the ground this many in game minutes, it could start to draw a horde",

How much INGAME time is takes to a body start sending "signals". If you set this to 60, for example, the body will be ignored for an ingame hour before start attracting zombies. Bodies that are next to each other are considered a "pile", and therefore, start sending "signals" counting from the oldest body in the ground.

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Sandbox_MaxHordeDrawWaitTime = "Maximum Time Body Exists Before Horde",
Sandbox_MaxHordeDrawWaitTime_tooltip = "Once a body has been on the ground this many in game minutes, it will attempt to draw a horde at least once",

The MAXIMUM INGAME minutes a body can stay on the ground without sending a signal (with other corpses around if there is). The previous setting and this setting determine the time range of when the signals are sent to attract zombie hordes from afar. If you set the previous setting to 30, and this to 60, for example, it means that the body pile will take between 30 ingame minutes to 60 ingame minutes to attract a horde to the body pile location.

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Sandbox_HordeGlobalCooldown = "Horde Global Cooldown",
Sandbox_HordeGlobalCooldown_tooltip = "Minimum in game minutes that must pass globally before any new hordes can form"

After a signal is sent to attract hordes, this setting will determine how much time it will WAIT before send another signal. Also, if horde settings is OFF, this can be ignored.

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As mentioned, most of settings is ignored if the horde setting is DISABLED.