21.   Scientists have long understood that animals use pheromones as a primary means of communication.

22.   Scientists understand that better than those of us who just cook.

23.   Second, the ability of distant computers to interact in real time makes the process so complex that even scientists cannot understand it without visualization.

24.   Scientists could not understand how it could have shown up in Indonesia.

25.   Scientists do not understand why minocycline appears to help some arthritis patients.

26.   Scientists have long understood that drug addiction involves brain cells that also play a role in the formation of memory.

27.   Scientists understand a lot about volcanoes.

28.   Smell has been hard for scientists to understand.

29.   The idea is that some of these disease-causing genes may have a purpose that scientists do not understand.