Here are two images showing two different events. The person who took these pictures claims that they used the bathroom for the last time at night and prior to leaving they didn’t see the marks but they saw the marks the next morning prior to using the toilet again. Let’s (for now) assume that this person’s claims are true, and one of those claims is that no one else uses that bathroom. The black marks can be wiped off. Your task is to tackle what those dark marks are, please and thank you.