Convenient Invitation

Mrs. Jones was reading a letter at breakfast. Suddenly she looked up
suspiciously at her husband.

"Henry," she said, "I've just received a letter from mother saying she
isn't accepting our invitation to come and stay, as we do not appear to
want her. What does she mean by that? I told you to write and say that
she was to come at her own convenience. You did write, didn't you?"

"Er, yes, I did," said the husband. "But I couldn't spell 'convenience,'
so I made it 'risk.'"