When at Undyne's house, after she asks you to select a drink, you can select her.

She will respond with,"Are you hitting on me?"

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When first encountering Flowey, you can choose to dodge the "Friendliness Pellets,"

He will eventually say,"Just run into the BULLETS" then backspace and rewrite it as,"Friendliness Pellets."

Then if you continue, he will say,"You know what's going on here. You just wanted to torture me."