Literally the very simplest way for a computer to disguise itself as human is to emulate natural language patterns.
I'd like to see the computer that, under current constraints, gets asked to provide a word and responds with "beptoptipalparopaladropa".
The year is 2050. Androids that superficially resemble humans roam the streets, murderbotting the shit out of people.
Murderbot: "Don't shoot! I'm human!"
Survivor: "How can we know?"
Murderbot: "Well, uh, I believe in love?"
I guess it's safe, then. It said the L word.