Leaf slug. that would be my pick....those things can squeeze themselves into the smallest spaces. simply because they are so tiny themselves, and they actually dont leave trails very often-the trails are so small so they are hard to see, or get covered by dust etc quicker. The damage on the bud is certainly the work of a slug. And if the plant is inside, the animals metabolism will increase, causing it to be more active, but also decreasing its life span.