The idea with the man-in-the-middle attack there is that the words would be different, say Alice and Bob want to talk but Eve MitM-ed them, as she always does.

The idea with the man-in-the-middle attack there is that the words would be different, say Alice and Bob want to talk but Eve MitM-ed them, as she always does. Alice sees "pink elephant salad" and Bob sees "piano lamps". They say the words, Eve has to reply in Alice's voice to Bob with "piano lamps" and then respond to Alice with "ping elephant salad". However then Alice makes a joke wondering if elephants like to eat pink salad. Bob will wonder as perhaps he wanted to remark how so few people play pianos these days. So Eve has a bit of a harder job if say instead it was just "1234" vs "5678" being said.