Regular sex.
A young couple were married and they were having sex all the time during their honeymoon.
When the honeymoon was over they had to adjust their sex schedule to their work schedule. So every day the husband would get home at 5 o'clock, and every day they would go to bed at 5:15.
This went on for months, never missing a day until the wife came down with the flu and went to the doctor to get a flu jab..
The shot killed all the germs inside her except for three. These three germs were huddled together inside her body talking over their survival plans.
One germ said, "I am going to hide between two toes on her left foot. I don't think the antibiotics will find me there".
A second exclaimed, "I am going to hide behind her right ear. I don't think they'll find me there."
The last germ said, "I don't know about you guys, but when that 5:15 pulls out tonight, I'm gonna be on it!"