At his introduction, Riva says that he is deaf due to a genetic mutation similar to the House of Hanover "all of whom had hemophilia." In reality, hemophilia showed up first in Queen Victoria's son Leopold, almost 200 years after the founding of the House of Hanover in 1636, and two of her daughters (Alice and Beatrice) were known carriers of the gene but it appears to have not affected any of her other seven children. However, the subsequent marriages and lineages from Leopold, Alice, and Beatrice carried it throughout the royal families of Europe and Russia giving it the nickname "The Royal Disease." It is considered one of the great mysteries of royalty as to why Queen Victoria had the gene for hemophilia as neither her father nor mother had that gene.
After giving Geordi, who is blind without his visor, an eye exam, Geordi asks Dr. Pulaski if she is done. She nods silently before he puts his visor on. However, it is a common and automatic response to make similar expressions of body language (such as nodding or shaking the head) when talking to blind people. When dealing with someone whose perceptions are as heightened as la Forge's, it even more understandable.
When Data is interpreting for Riva, he speaks the words before Riva signs the word. He also signs words to Riva before Captain Picard speaks them.
When the chorus says "I have been expecting you" it is the female voice speaking the words. However, the female member of the chorus does not move her mouth.
In the initial meeting with Riva, when Counselor Troi is telling him how beautiful his chorus sounds, you can clearly see a crewman on the left side of the screen. He is wearing khakis and a polo shirt.
When Picard refuses food and refreshment from the chorus member when first meeting Riva, some equipment or possibly a crew member's hand appears on the left edge of the screen.
In a peace negotiation, it should have been obvious that weapons would not be allowed for the negotiating parties. The two sides should have been told ahead of time not to bring weapons and, as a security detail, Riker and Worf should have checked all involved for weapons before allowing them near the mediator.