A pickle

 is the thirtieth level of Even More Bloons. To complete the level, pop the lower row of the Helium Bloons then pop the middle row then pop all the Spikey Bloons. Surprisingly, the spikes can pop both the top row jars and the bloons in a single fall, and this could be that the spikes travel at a slower speed at first row thus making the spikes have more time to contact the first row helium bloons.