Yeah, chocolate is actually poisonous for dogs (and, by virtue of being technically the same species, wolves) in anything but so exceedingly miniscule amounts that you might as well not have given any to begin.
I was somewhat disappointed for a second after seeing it was just Kagerou's dream, until I realized they're still sleeping in the same bed together (wonder how that works with a mermaid).
From what I've seen in many Yuri pictures... Nope. Well some did it to embarrass another, feel dominant, or joke around. If u talking IRL, in my case, never played