[Kotlin] I'd like to ask you a question about accessing child instance properties of the parent instance type.

to study inheritance at Cotlin I'm asking you this question because there is a confusing part of the child instance property approach in the parent instance

open class Animal(val size:Int)

class Spider(val poison:Int): Animal(50)


fun main() {
        val a1:Animal = Spider(5)
        println("posion : ${a1.poison}")
}

where a1 is inaccessible to poison. Because a1 is an animal type

Creating a child type in a parent type in an inheritance relationship?Parent instances only for parent type properties

I learned that it's accessible

By the way,

open class Animal(val size:Int)

class Spider(val poison:Int): Animal(50)


fun main() {
        val s1 = Spider(5)
        val a1:Animal
        a1 = s1
        println("posion : ${a1.poison}")
}

Why is this accessible?

a1 was created as an animal type.

I don't understand.