Final answer:
Sudden noises like breaking glass or loud crashes in a noisy environment are likely to draw a person's attention away from their conversation due to bottom-up processing.
Step-by-step explanation:
While having a conversation with a friend in a noisy, busy coffee shop, the most likely thing to draw Nina's attention away from her conversation would be a sudden, unexpected noise, such as the sound of breaking glass or a loud crash. These sounds are likely to penetrate Nina's attentional filters in a process known as bottom-up processing. Our attention can be captured by loud or sudden environmental noises that stand out against the background hubbub, prompting an involuntary shift of our attention towards the new stimulus.