Is it possible that cats literally make a person crazy? Czech scientist Jaroslav Flegr thinks it is possible based on his research of the single-celled Toxoplasma gondii parasite. This article from The Atlantic digs a bit deeper into his findings, the scientific communities reaction to it and just how much the little protozoan can affect a human. Turns out, "crazy" is maybe a bit harsh of a term but the theory is that it can change the connections of neuron connections, altering your natural response to particular stimuli.

All and all, it's only one article about the research performed by one guy and it may not even be the least bit worrisome. Despite all that, it's interesting to think about - your standard house cat may actually be having a legitimate influence on their owner through cellular means.