system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Can you alter someone's dream by touching or talking to them while they're dreaming?

And if the answer is yes, is it possible to find out how the dream can change?
gpt
If you're subtle enough to not wake the person up, yes you can absolutely affect their dreams. Even while you are asleep, many of your senses are still functional. Your ears for instance never really turn off. You still hear everything around you even while you sleep and what you hear will absolutely influence your subconscious. That can translate to altered dreams. 

As for finding out how it affected the dream, you'd have to ask the dreamer.