yeah he was chewing on his boot and the ears had to have blood on them and infected blood in your mouth is enough to turn you?
for instance: cop + glenn cover selves with zombie guts so zombies with the exceptional ability to smell the living from far away wont smell them: theyre on the freeway hiding under cars two feet from the infected and the zombies cant smell them for some reason. or getting sprayed with zombie blood in the eyes / nose / mouth area - they dont turn. or black dude gets his arm gashed then has bloody zombies laying on top of him but he doesnt get infected.
but it seems like the main thing theyre going on is the infection is in their brains, and passed by bites. if daryl gets infected from the ear touching his mouth im going to call serious bullshit and might even stop watching the show.