“But how lovely, she said, taking his flowers. She understood; she understood without his speaking; his Clarissa. She put them in vases on the mantelpiece.”
After recieving the flowers, Clare says something, but the following sentence shifts to belong to someone else’s. Richard though, “his Clarissa”. So in this sentence, he’s thinking about her understanding. He even pushes it further, knowing she understands without speech. It leaves out Clarissa’s own thought at this moment and makes a strange twist to possibly make them seem more unified in this moment. Their thoughts could be the same. He may actually know that she understands and Woolf is showing the reader that they don’t need speech to understand eachother.