"For instance." From his position at the blackboard, the poltergeist lectured his captive audience of one. "Your average pigeon is polyamorous."
Frozen at his desk, Dean could only stare in horrified disbelief.
"Unlike the paltry human, pigeons aren't restricted to one mate." The long-dead ornithologist coughed, embarrassed. "They enjoy multiple partners throughout their lifetimes."
On that indelicate note, Sam appeared in the doorway.
Oblivious to the impending rescue, the ghost continued. "Now, on to the pituitary gland."
Sam stared. Snickered.
Dean started to steam.
"Or, as I like to call it, the pit bull of the endocrine system."