Joke of the day

I heard this joke from Yes 93.3. I found it's a funny one :)
Hope it does make your day too.......

An old man went to see doctor.
The doctor told him, you need eight hours to see the effective `有效' after taking the medicine.

He took his medicine & went home.

The old man son came back from work.
He heard his dad keep laughing.....

Hahahahahahaha...........
Hahahahahahaha...........
Hahahahahahaha...........

He went to ask his dad.
Father, why you laugh for non stop?

The old man replied, Doctor told me to laugh `效' for 8 hrs.

If you heard it in Chinese, it's more funny ;)