When Basil is explaining to Polly that Mrs. Richards' money is ten pounds up on the deal, a crew member is seen briefly scuttling about on the office floor behind him, they bump the office door causing it to move a little behind Basil.
When Mrs. Richards says "I'm not listening to anymore of this rubbish..." and walks into the dining room, the shadow of a boom mic and other equipment is visible above the dining room door.
Soon after, Mr. Fawlty tells his guest he'd "better hurry, the tide leaves in about 6 minutes" a Boom mic is clearly visible.
When Sybil throws a cup of coffee over Basil at the end, about half of the contents miss him and splash over the major standing behind him instead. The actor tries to make the best of the situation when having his jacket soaked, especially in the following shot.