Class methods are executed as static why?

Question

PHP

I ran into an amazing problem. I have a class that has a couple of methods.
Example

class Response {
  public function execute() {
    return 'thing';
  }
}

in another place it was possible to call it like this
Response::execute()
. But Response->execute () does not work, it gives an error.
I create $r = new Response, the same troubles.
This is how they both work

echo Response::execute();
echo "\n";
# thing
$r = new Response;
echo $r->execute();
# thing

What the hell is this

Answer 1

Turn on the output of all errors and you will see
As well as

$arr = [];
echo $arr['some'];

does not generate errors if disabled

Answer 2

Response::execute() is a legacy of the past, don't do it this way.

$r = new Response;
echo $r->execute();