this is (also) not my dog

When i first moved to Taiwan, i asked some Americans what the country was like.

One said:

A little boy wanted to stroke a dog, but was worried it might bite.

So he asked the man with the dog 'Does your dog bite?'

The man said no, his dog didn't bite.

So the boy stroked the dog, which promptly bit him.

'I thought you said your dog doesn't bite.'

'It doesn't,' the man answered, 'but this is not my dog.'