My first cat used to sneak into my cupboard and sleep in there. I had no idea until one day I got home from work and was making supper. I reached into the cupboard to grab a plate and felt something big and furry instead.
I (must of) must have sounded like a 10 year old school girl. Nearly ended up being an unscheduled laundry day.
"Must of" isn't a thing, and you should understand that without someone pointing it out. Same as "could/should/would of" isn't correct.
Learn basic grammar.
