glass 1/2 something

Greg, "You're kinda a 'glass half full'"
Val, "I'm more realistic, you're more optimistic."
Yoda, "What are you talking about?"
We explain the idea of glass half-full vs. half-empty to Yoda. 
Mimi chimes in, "Well, glass half-full means it was only poured with half of the amount of liquid it can hold.  But glass half-empty means someone drank half of it."
Miss Mimi, our little scientist!