While my mother was in hospital recently I managed to pick up Norovirus, it had to be from the hospital when I was visiting, where else?
Now that is joy beyond your wildest dreams, the pain is incredible. The point I was going to make though, without being too indelicate. The power that the colon has when it wants to use it is quite considerable. In normal use the body becomes lazy as we get older, hence the need for straining.