Eventually you just have to admit that if it looks like the absence of a duck, walks like the absence of a duck, and quacks like the absence of a duck, the duck is probably absent.
I agree subject to the specification that each such observation must look substantially more like the absence of a duck then a duck. There are many things we see which are not ducks in particular locations. My shoe doesn't look like a duck in my closet, but it also doesn't look like the absence of a duck in my closet. Or to put it another way, my sock looks exactly like it should look if there's no duck in my closet, but it also looks exactly like it should look if there is a duck in my closet.
Another monthly installment of the rationality quotes thread. The usual rules apply: