Sox 6. Actually yes. They don't make noise and are small enough to easily miss. To expound on what FH 1100 wrote; preflights are done in the dark with a flashlight. Examining the inlet area is fine, but our little friends can stick to anything, so finding them on the side of the fuselage or even the bottom of a rotor blade has happened. More than likely, its the frog that ended up on the doghouse or the top of the cabin that ends up getting sucked in once the airflow breaks him loose. Using your flashlight, you try to look everything over but, like the bird strike, it's possible to not see it.
Fortunately alligators are too big to fit in the inlets so we're safe there.