Endler Stuck IN Filter!?!

The other night I was taking a look at one of our 10 gallon tall tanks. We realized that the endler that was in there was missing. We dismissed this because it is not rare that we cannot find him. The next day comes around and he is still not in the tank. Since endlers *can* jump, we looked around on the floor. We do have a lid on the 10 gallon tall tank, but he could have somehow found a way to squeeze through a crack or something. We couldn’t find him on the floor either! Another day gone without seeing the endler. How could he have just disappeared? We do a water change two days later. Taking off the lid to the hang-on-back filter, I saw a little movement in the compartment where water goes into the filter. I catch more movement in the corner of my eye. The endler was alive!! He looked like he was just chillin’ in the small area. We immediately used our hands to scoop him out of the filter and into the aquarium where he can see his friends again! How and why did he get into the filter? He is now recovered from his injuries from inside the hang-on-back filter.