... My sister has been the most negative by far- normally a very intelligent human, she first stated that she would never come over if I got one, and has insisted since then that Horatio is plotting to eat me, and one day he will decide it is time to make me dinner and thus will grow sufficiently larger by sheer force of will. I did make her meet him, and she is perhaps not so negative now, although she still insists that he's plotting... Something. ....
That sounds like she fell for the old myth that a snake lying next to you is somehow "measuring you" for consumption. Maybe she picked that up from someone
when she was much younger & it's still there subconsciously?