But the mistletoe is far more than the decorative fixture it's become known as today and can actually be extraordinarily powerful depending on where you get it from. There are over 1,500 species of mistletoe, some of which are toxic and can cause blurred vision, vomiting, and even cardiac arrest (and here we thought compulsory public holiday smooching was enough to induce feelings of nausea). In Norse mythology, it was a symbol of peace and friendship, and the plant has been used medicinally in Europe for centuries when treating epilepsy, infertility , hypertension, and arthritis. In recent years, according to Costin, it has even been integrated into clinical trials for cancer treatment albeit not so successfully. "Although some trials indicated that mistletoe improved survival or quality of life," he says, "almost all of the trials had major weaknesses that raise doubts about their findings."