Ghostbusters star Kate McKinnon didn't know what a condom was

Kate McKinnon mistook a condom for a "new species of sea plant".

The Saturday Night Live star used to love finding the "fruits of the sea" on the beach when she was young and couldn't understand why her mother didn't want her to keep the "white seaweed" she'd discovered.

Asked by Scarlett Johansson for her favourite childhood memory, she recalled: "I grew up in a town on Long Island, and there was a little beach on it.

"I loved the ocean so much, and I loved to pick up little snails, find little dead crabs, and pore over the fruits of the sea that had been left on the beach.

"One day I was so excited, because I had found a piece of what I assumed was white seaweed.

"I thought, 'Wow, I'm an intrepid explorer and I've identified a new species of sea plant. I'm incredible.'

" I ran over to my mom and I was like, 'Mom, look! It's white seaweed!' She was like, 'Why don't you put that piece of white seaweed back in the water, or better yet, throw it in the garbage?'

"Because it turns out it was a condom, and I didn't know what a condom was.

"I thought, 'Why doesn't she want me to have this white seaweed? She's afraid of the unknown, I guess.' "

Elsewhere during the chat with Interview magazine - in which she was asked questions by her famous friends - the 35-year-old actress praised Ellen DeGeneres for her "unbridled courage" in coming out as gay at the height of her fame because it "paved the way" for Kate and other stars to be themselves.

Kate - who is also a lesbian - was asked by the talk show host for her three favourite things about her and replied: "Over the course of appearing on your show over the years, you have given me my best blazers, shirts, and sneakers.

"I always leave with a little Ellen DeGeneres-brand parting gift.

"Then, obviously, there's your unbridled courage, which has paved the way for me and countless other people to be who they are. I owe you my life in that respect.

"And then there's the lengths to which you'll go for your cats, which rivals my own."