My dumbest animal mistake was playing can have my finger with a 4 foot moray eel on display wile working at an aquarium shop. All the guys there used to play "can't have it" with our fingers when ever we cut ourselfs. The eel only won once but it was more then enough.
My worst reptile husbandry mistake was not a newbie one but one made recently ... complacency and big headedness (if headedness is a word) anyways I had gotten a female Dumeril's boa and set her up in quarentine but did not put in a hide shelter, two weeks alter I fed her her first meal in my care and I will admit it was a little large. anyways because she had no hide I am assuming she was very stressed and well she regugitated (spelling ??? again) after she regurged she was very limp, she died later that evening
So my mistake was complacency! Hangs head in shame....
