I doubt it was travelling over the moat.. i would move their pen away from fires,lox and as advised forges smelters etc or (Halstein and the trader wards..(ticket lodged for non breeding boars n wolves) ) you slowly can work out what it is by moving them a few times till when they are NOT frightened.. they dont seem to eat yellow mushrooms so thats interesting concept @PakaNoHida .. i have backup animals a long way from base in case of epic failure! :-) edit: you may have a lurker..after raid events a skel or drauger may be in moat or similar?