It's unacceptable to mar the food of someone else.
Delia loves the taste of lamb but her husband Roger refuses to even try any.
Delia wants to show Roger how good lamb can be.
Delia cooks her favorite lamb dish and asks Roger to try one bite and tells him he doesn't have to eat any more if he doesn't want to.
Delia makes spagheti for dinner but secretly uses lamb instead of beef without telling Roger, so she can prove he actually likes lamb.
Roger agrees to try the dish and ends up loving it.
Roger is angry when Delia reveals that the food had lamb in it and loses trust is Delia.