Just waiting to get in.
Its usually the Cuban tree frogs, which are ugly little things. They fall into the plumbing vent and swim up the P trap in the toilet and stick to the side. I have had a few irate people call me about how they got a surprise while sitting on it in the morning. Don’t let this happen, get some Critter Quitters ate Homedepot.com or Amazon, or call one of our installers at critterquitter.com