Is that a joke?

If there is one thing that tests a mothers patience more than anything else it's getting a 5 year old to understand the concept of a joke.

For some reason they just can't grasp the whole double entendre concept. Like, duh.

'Mum! Mum!'

'Yes darling'

 'Why did the fox go to the woods?

'I don't know, why did the fox go to the woods?'

'Because he was hungry. Is that a joke?'

'No, that's not a joke'.

30 seconds later...

'Mum! Mum! What did the baby say to the Mummy?'

*sigh* 'I don't know what did the baby say to the Mummy?'

'I'm a baby. Is that a joke?'

'No, that's not a joke'

2 minutes later and I'm still reading the same paragraph in the paper for the thirtieth time....

'Mum! Mum! Why did the cow cross the road?

'I don't know why did the cow cross the road?'

'Because he wanted to cross the road. Is that a joke?'

Shoot me now. Please.