What happens when the Buddha Sneezes? rules get made.
Did you know monastics aren’t allowed to say “bless you” to each other? One of those interesting rules you find when you deep dive the Vinaya :
Now at that time the Lord, surrounded by a large assembly, sneezed while he was teaching dhamma. Monks, saying: “Lord, may the Lord live (long), may the wellfarer live (long),” made a loud noise, a great noise; the talk on dhamma was interrupted by this noise.
Then the Lord addressed the monks, saying: “Now, monks, when (the phrase) ‘Long life’ is spoken to one who has sneezed, can he for this reason live or die?” “That is not so, Lord.” “Monks, ‘Long life’ should not be said to one who has sneezed. Whoever should say it, there is an offence of wrong-doing.”
Now at that time people said “May you live (long), honoured sirs” to monks who had sneezed. The monks, being scrupulous, did not respond. People … spread it about, saying: “How can these recluses, sons of the Sakyans not respond when (the phrase) ‘May you live (long), honoured sirs’ is being spoken to them?” They told this matter to the Lord.
He said: “Monks, householders like lucky signs. I allow you, monks, when (the phrase) ‘May you live (long), honoured sirs’ is being spoken to you by householders to say, ‘Long life’ (to them).”
So as you can see responding to someone who sneezes is very very ancient, and to the Buddha superstitious, as this will not effect whether the person lives or dies, but out of compassion and courtesy, monastics can respond back when someone else says it to them.
While I know some monastics don’t see it this way, I always encourage laity to read the vinaya and know at least the basics of the rules, as this will inform you on how a monastic should act and what rules constrain them. Plus reading the Vinaya gives you an interesting glimpse into the culture of the time in ancient India, with plenty of shock and giggles.