Probability Interpretations Puns

(Technically I haven't heard any joke before, but...)

I was telling my dad about tactile sign, which is what deafblind people use to communicate. It is like signing condensed ASL with someone's hands on yours, and it is what I plan on specializing in when I am a Certified Deaf Interpreter. He brought up Helen Keller and the conversation went as follows.

Dad: "But how many people can really do that? How many people could really communicate with Helen Keller?"

Me: "Well-"

Dad: "PROBABLY JUST A HANDFUL!"

I'm borderline convinced he deafened me as an infant in hopes that someday the set up for this joke would present itself.