Bats

Firstly - I said that "The Flincher" sounded like bats, not exactly the same as some bats. More specifically, if there was a known breed of bat that grew up to ten metres, I might pursue this theory further. However, it would have taken an enormous quantity of bats to produce the draught created by one "Flincher".

Add to this that, in the countless hours of wandering around the hospital, none of us had ever encountered any bats (and if they did use the place, there's a good chance we'd have seen them asleep during the day). Also, although a "bat draught" might create some noise, it couldn't be comparable to the sounds we heard. What then, if a large bang (such as the one I recall) had startled some bats and they flew towards us? It's a good case point, I must admit. The fundamental problem, however, is that the volume and intensity of the howling, and sheer power of the Flincher's draught (not to mention the feeling of evil), simply could not physically have come from even a sizeable group of small nocturnal mouselike winged mammals. The technical plausibility of the "bat theory", then, realistically rules it out.