Hi BYC friends! This is my first hatch and I’m on day 21! I have 9 duck eggs (4 mallards, 5 runner) and they all appear to be moving and progressing as expected. One egg, however, has a peculiar black spot inside. Any thoughts on what this might be (see pic and short video)? I am turning the eggs and have the temperature right at 100 in a still-air incubator. Humidity is about 55%.