Little Johnny is complaining to his mother early in the morning

'Mum, I have a stomach ache...'

'Don't worry, honey,' says the mother. 'It's only aching because you have an empty stomach.'

Little Johnny acknowledges this and calms down. In the evening, Little Johnny's parents welcome an esteemed guest: the Under Secretary of Interior. During the course of the evening, the Under Secretary says:

'Dear Madam, could I get some painkiller please? I have a horrible headache...'

Little Johnny looks up from his drawing in the corner and says:

'Don't worry, sir! It's only aching because you have an empty head!'