A joke about biology

Xiao X goes to Bird Market. Found a parrot with a price tag of 3 yuan money.

So he asked the seller: Why is your parrot so cheap?

Vendor: My parrot is stupid! Shit, I've been teaching for a long time. Up to now, I can only say one thing-"Who is it?"

Xiao X thought it was cheap anyway, so he bought it.

When he got home at night, he thought, "I don't believe in teaching, and I don't believe in teaching!" " "So little X taught it to say something else all night. But in the morning, the parrot still just said, "Who is it? "So little X got angry and locked the door to go to work.

After a while, a gas collector (Z for short) came.

Little Z, "Knock, knock ..." (knocking at the door)

Parrot: Who is it?

Z: gas inspector. Parrot: Who is it?

Z: gas inspector. Parrot: Who is it?

Little Z: Check the air. In the evening, little X came back. I saw a man lying on the ground in front of my house, foaming at the mouth.

Little x: yo ~! Who is this?

I heard it in my room: the gas inspector.