Board Thread:Questions and Answers/@comment-71.8.106.27-20151125020357

This is probably a noob question but this is my first bloons game (Bloons TD Battles), I was just playing someone who had a monkey apprentice and a couple of cobras and I was looing -2 health every few seconds, although no balloons were passing my defences. Anyone know how to prevent this or defend against it, was it something my opponent was doing?

Thanks. 