As your taste buds start coming back you'll probably over-vape a carto less. You probably did burn it, but you can't necessarily go by color. If you try to refill a burnt carto the juice won't absorb, but will "puddle" in the center no matter what you do. Another reason for the initial 5 drops (better 5 drops wasted than 20). A too full carto will indeed make a bubbling sound. Just take it off of the battery and blow gently into a paper towel to clear it out.