Cactus, Cacti, Cactow

I recall my first day in Psych 1 way way back in  college. The classroom was set up seminar style with large round tables and we all entered and began to jockey for position. The professor walked in with a box under his arm and stopped at each table and pulled from the box a tiny moon cactus which he set in the center.  He didn't say a word, but after the last table he walked to the board and began writing his name, the name of the class and reading assignments. In the curious quiet of the classroom a voice suddenly said "ouch!"

Our Professor turned from the board with a big grin and said "Now we can start!  People, Psychology is really just the study of human nature. So what is human nature? Mostly driven by our intelligence, it is a curious search for our boundaries in nature and society. Now on each table is a cactus, a small desert plant.  A hawk flying though the desert might decide to land and as it drops down it sees the cactus and says 'Uh oh, spines, which are probably sharp' and so it glides on over to land on a rock.  A lizard scurries along looking for shade, but sees the cactus and says 'Oh, spines, hmmm, and probably sharp' and takes cover in the shadow of a rock instead. A snake slithers along and seeing the spines of the cactus, decides they might be sharp so it slithers up the dunes instead. Then along comes the most intelligent creature on God's earth,  a human
being, out hiking. The human sees the cactus and says 'Oh, spines...... Ouch; and they are sharp!'
That people is human nature."