“Attitudes are contagious. Mine might kill you.”

“A positive attitude is contagious. So is the lack of one.”

“A healthy attitude is contagious but don't wait to catch it from others. Be a carrier.”

“I'll leave you two alone. Morality might be contagious.”

“Other people's views and troubles can be contagious. Don't sabotage yourself by unwittingly adopting negative, unproductive attitudes through your associations with others.”

“...and suddenly it occurred to him that the birds, whose twitters and repeated songs sounded so pretty and affirming of nature and the coming day, might actually, in a code known only to other birds, be the birds each saying 'Get away' or 'This branch is mine!' or 'This tree is mine! I'll kill you! Kill, kill!' Or any other manner of dark, brutal, or self-protective stuff—they might be listening to war cries. The thought came from nowhere and made his spirits dip for some reason.”