Does a Snake Sword user get an AoO for an opponent moving from one threatened square to another within range?

Question

So I am starting a new character in an ongoing campaign and I was going to do a Chain Armor + Spiked Chains dual wield trip tank deal but I decided to see what other reach type weapons might be available (due to not liking the chain armor penalties and also for RP purposes I didn't like the look of the armor....) and I thought of a Snake Sword (think Ivy from Soul Calibur) and then I found the 3.5 variant Snake Sword and my DM approved it and I'm just curious how the AoO works for that.

I was reading a few different movement based threads and such online and it said on one that moving from a threatened square is of course an AoO so I am curious:

If I threaten 15ft in every direction, does that mean that them moving from say my 15' threat square to my 10' threat square trigger an AoO?

AoO triggers reference: https://roll20.net/compendium/pathfinder/Actions%20In%20Combat#content (under Move Action/Move)

Answer 1

Yes, if you are able to make Attacks of Opportunity with a whip

Moving from a square within 15ft to another square within 10ft of your threatened area counts as moving out of a threatened area and will trigger an Attack of Opportunity.

You may only trigger a single Attack of Opportunity per action (and per movement), so a creature waltzing in your threatened area (a Move Action) will only trigger a single AoO from you, even if you have Combat Reflexes or similar abilities.

For a visual reference, see this video explaining Attacks of Opportunity, do note that the very last example is probably wrong, he wouldn't get a second attack unless that was a second Move Action.

Finally, note that Whips do not threaten enemies within your attack reach in Pathfinder. You need certain feats for that, such as Improved Whip Mastery, or also house rule that part of that item.

The whip is treated as a melee weapon with 15-foot reach, though you don’t threaten the area into which you can make an attack.

Answer 2

Generally, if a creature threatens a 15 ft. area around it and a normal foe takes a regular move action to move from 15 ft. away from the creature to 10 ft. away from the creature, the foe provokes an attack of opportunity from that creature. Thereafter on its turn, the foe typically continues its movement within the creature's threatened area normally, not provoking further attacks of opportunity for its normal movement.

The foe's act of moving out of one square the creature threatens so as to provoke an attack of opportunity from the creature is enough to prevent the creature from making further attacks of opportunity against that foe in response to the foe—this turn—moving out of more squares the creature threatens.

(A foes can avoid provoking attacks of opportunity for its movement by, for instance, taking a 5-ft. step or by making a Tumble skill check.)

However, in the case of the homebrew snake-sword that the DM's approved, while it is in whip mode, the snake-sword's wielder does not threaten an area with it, despite the wielder being able to make attacks against foes up to 15 ft. away. That's because it functions—unless the GM rules otherwise—like a normal Pathfinder whip. The snake-sword description makes specific exceptions to the way melee weapons normally threaten an area.

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Note: The whip is widely considered a sub-par weapon. (See also here.) While the snake-whip has some advantages over a regular whip—dealing lethal damage to armored target is certainly a good start!—, this player suspects a PC wielding a snake-sword will find himself using the snake-sword in longsword mode far more often than in whip mode.