Why is there always a little bit of shampoo/shower gel left in a bottle that doesn’t come out even if you shake it a

Question: Why is there always a little bit of shampoo/shower gel left in a bottle that doesn't come out even if you shake it a lot or leave it for a while?
- Keywords:
  bottle,
  soap
Asked by nisai1 to Ben, Dave on 28 Jun 2013.
- David Briggs answered on 28 Jun 2013:
  
  Because life is just like that 😆
  
  It’s down to the design of the bottle. The shampoo is so viscous and sticky that it would rather cling to the bottle than let go and let gravity take control.

Question: Why is there always a little bit of shampoo/shower gel left in a bottle that doesn't come out even if you shake it a lot or leave it for a while?