Starting a zoo

Murphy decided to find an interesting hobby. Animals appealed to him so he wrote to the local pet store.

'Dear sir,

I'm starting my own zoo and would like you to send me two mongooses ...'

He looked at the spelling and thought, 'That's not right'. So he wrote: 'Send me two mongi'. That looked even worse. '... send me two mongeese.' No, that was worse still. In the end, though, sanity prevailed and he wrote:

Dear sir,

I'm starting my own zoo. Could you please send me a mongoose.

PS. And could you send me another one?