George arrives home to find Lynne crying. Lynne says it is only a few tears. George tells he will take Lynne out to dinner to cheer her up. Lynne says that manipulating your man is knowing your onions whilst chopping onions.
To explain this episode we must jump to the end. Lynne has foxed George into taking her for dinner by cutting onions which have made her cry. She has orchestrated this entire event to both get out of making dinner and and get taken out to dinner. She has done a good job at it as her entire plan has worked.
The main question here is why does she go back to cutting the onions? She has won. She should be upstairs getting dressed for her dinner. But instead she goes back to the onions which will make her cry more and she will be wasting a perfectly good onion. The fact is that the onions only provide Lynne with a limited amount of tears. In order to keep up the charade she must continue to cry a bit until she goes upstairs. She will also need to come up with a reason why she is crying as the smell of onions will soon enough make George a little suspicious.