I mean that if there are 24 people, and all of them have a collar attached in their neck. You have to collect 5 of these collars to leave the island. And the collars can be taken off only if its carrier dies. So basically:

To get out of the island, you have to kill 5 people. ;)

The collars are waterproof, shockproof and are indestructable.

And if there are 32 characters in game, you have to collect 7 instead of 5. No matter the number, in the end, only 4 will survive.

You can team up, make friends, or kill everyone you see, it's up to you!