Quick Question on Traits

error: invalid call to 'hello': argument #1 cannot be converted from 'Dog' to 'Talkable'

trait Talkable:
    fn hello(self, thing: Talkable) -> String: ...
    fn goodbye(self, thing: Talkable) -> String: ...
    fn get_name(self) -> String: ...

struct Person(Talkable):
    var name: String
    fn __init__(inout self, name: String):
        self.name = name
    fn hello(self, thing: Talkable) -> String:
        return self.name + " says hello to " + thing.get_name()
    fn goodbye(self, thing: Talkable) -> String:
        return self.name + " says goodbye to " + thing.get_name()
    fn get_name(self) -> String:
        return self.name

struct Dog(Talkable):
    var value: __mlir_type
    var name: String
    var nick_name: String
    var age: Int
    fn __init__(inout self, name: String, nick_name: String, age: Int):
        self.name = name
        self.nick_name = nick_name
        self.age = age

    fn hello(self, thing: Talkable) -> String:
        return self.name + " barks at " + thing.get_name()    
    fn goodbye(self, thing: Talkable) -> String:
        return self.name + " barks at " + thing.get_name()
    
    fn get_name(self) -> String:
        return self.name

# I also tried this from documentation
# fn say_hello[T: Talkable](t1: T, t2: T):
#  t1.hello(t2)


fn main():
    var s = Person(name="Jim")
    var d = Dog("spot", "dog", 2)
    d.hello(s)
    # say_hello(s, d)