What is the difference between calling super and calling super()?

In Ruby, `super` and `super()` are related but serve different purposes. Both are used in the context of inheritance and method overriding.

1. **`super`:** This is used within a method of a subclass to invoke the same-named method from its superclass. It passes the arguments that were passed to the current method in the subclass.

```ruby
class Parent
def example(arg)
puts "Parent class, arg: #{arg}"
end
end

class Child < Parent
def example(arg)
puts "Child class"
super # invokes the 'example' method in the Parent class with the same 'arg'
end
end

Child.new.example("Hello")
```

In this example, `super` is used to call the `example` method of the parent class with the argument passed to the method in the child class.

2. **`super()`:** This is used to invoke the same-named method from the superclass but without passing any arguments explicitly.

```ruby
class Parent
def example(arg)
puts "Parent class, arg: #{arg}"
end
end

class Child < Parent
def example(arg)
puts "Child class"
super() # invokes the 'example' method in the Parent class without passing 'arg'
end
end

Child.new.example("Hello")
```

Here, `super()` is used to call the `example` method of the parent class without passing the argument explicitly.

In summary, `super` without parentheses passes along the arguments implicitly, while `super()` explicitly calls the superclass method without passing any arguments. The choice between them depends on the specific requirements of the overridden method in the subclass.