ok poo poo face. If you know anything of women, you'll know that they sync up their periods if they live in the same household or in a work place. Did the women 'catch' the period from other women? Or is there a subconscious biological thing that is happening? Same with a Virus. You don't catch the virus but your body may 'sync' up with someone who has it. By your argument, if one person in a house has the cold then everyone should catch it. However, that's not the case. Some people have a stronger immune system (obviously). Which speaks to Terrain being more important than Germs. If you're immune system is stronger than it doesn't matter if someone else is 'sick'.