Here's a snippet of the actual code:
1
2
3
4
5
6
7
8
9
10
11
12
13
on:use {
	if ($usethestone==1){
		local $stonecon=0;
		$stonecon+=count_inrange("item",89,150);
		$stonecon+=count_inrange("item",102,150);
		$stonecon+=count_inrange("item",103,150);
		if ($stonecon>=25){
		Activate teleporter...
	}
	else{
	Tell the user they can't
	}
}
Item 89 is "fish". (Not fried)
Item 102 is "clam".
Item 103 is "starfish".
So you could have 25 fish, or 10 fish, 5 clam and 10 starfish etc... It's not proportionate or anything. Just drop a total of 25 of these things near the stone and use (the 'E' key) the stone.