In Robert Browning's poem "My Last Duchess," Browning describes a duke who is speaking to the representative of a future wife for himself. This duke, as a sort of warning to the representative of his bride, shows the painting of his previous spouse, now deceased, and describes what he believes to have been her weak and flirtatious character. In doing so, he is able to convey the message of warning that his new wife had better be better behaved, or else.
In lines 12-19, he mentions that the representative might have noticed the coy and excited expression on the former wife's face in the painting. The duke says that many have wondered and asked that question, and that it wasn't her husband alone that made her appear to be so happy. Rather, she seemed to give delighted glances to a lot of people, for a lot of reasons. For example, the painter of the painting (Fra Pandolf) might have told her that part of the mantle in the painting was covering too much of her wrist, or that he was incapable of painting the flush of color along her throat. These little things that people said to her often made her blush with joy. The rest of the poem goes on to indicate that the duke highly disapproved of his wife's joyous behavior; he considered it inapproprate that she should be happy around anyone other than him. So, he "gave commands," and the wife, the reader has to assume, was killed. This was to warn his future bride that she had beeter not behave that way.
A bit bizarre, yes, but it certainly makes for an entertaining story for a poem. I hope that helped a bit; good luck!