"Then there was the great, the all-important point which, oddly enough, the prosecution never for a moment took into consideration.

When Chipps, the footman, first told Lavender that Lord Arthur could not see him the bookmaker was terribly put out; Chipps then goes to speak to his master; a few minutes elapse, and when the footman once again tells Lavender that his lordship won't see him, the latter says 'Very well,' and seems to treat the matter with complete indifference.
"Obviously, therefore, something must have happened in between to alter the bookmaker's frame of mind.

Well! What had happened?
Think over all the evidence, and you will see that one thing only had occurred in the interval, namely, Lady Arthur's advent into the room.
"In order to go into the smoking-room she must have crossed the hall; she must have seen Lavender.

In that brief interval she must have realized that the man was persistent, and therefore a living danger to her husband.

Remember, women have done strange things; they are a far greater puzzle to the student of human nature than the sterner, less complex sex has ever been.