Ads' grandma has been teaching him some slokas. In particular, the mantra of Lord Vishnu (Shaantakaaram bhujaga-shayanam) is something he can recite perfectly. He was suffering from night terrors a few months ago and started asking me every night "Will I get bad dreams?" and I always used to respond with a simple "No, you won't". His grandma told him that he would never get bad dreams if he recited the sloka before he went to bed. He obediently went about doing this and obviously (and coincidentally), the night terrors stopped. So he attributes his peaceful sleep to the sloka. He has started saying it diligently at all times of the day and night. For the last week, he has been starting every sentence with "Bhava bhaya haram" and often interrupts himself in the middle of a sentence to say the same phrase. It appears that it has become an emotional crutch for him.
I don't know whether to be (slightly) irritated or (highly) amused by this new idiosyncrasy. I think a strategy of placid indifference might just do the trick.