Don't use arrays ad hoc

example.php

// Do NOT do this
$animals = [ 
  'cat', 
  'dog', 
  null, 
  2 
]:

// DO do this
class Animal
{
    public string $name;
    public string $species;

    public function __construct( string $name, string $species )
    {
        $this->name = $name;
        $this->species = $species;
    }
}

$animals = [
    new Animal( "Leo", "Lion" ),
    new Animal( "Milo", "Cat" ),
    new Animal( "Bella", "Dog" )
];