9:56 PM PT -- Britney Spears just adjusted her caption, saying, "Don't worry they are NOT real knives!!! Halloween is soon!!!" Thing is ... you hear the clanging of the knives as they come together, so they sure seem real.

Britney Spears put her years-long fascination with knives on full display ... dangerously dancing with two massive butcher knives in a bizarre new video.

Spears posted the video Monday holding the razor-sharp blades with the caption, "I started playing in the kitchen with knives today" while she rubbed and even clapped the blades together while dancing.

The whole thing comes across as extremely dangerous -- as Spears clearly isn't trained to hold or handle the tools in such a manner ... at times jabbing them in the air.

While Britney claims she only started playing with the knives "today," we were first to report months ago Britney had a fascination with knives.

In fact, as her conservatorship came to an end, those responsible for her care made a list of recommendations ... one major rec being to keep knives away from her.

Multiple sources tell us Britney saw knives as a form of protection, afraid she's be re-institutionalized. We're told Britney keeps knives all around her house -- including in her bedroom -- and one source said she, "was paranoid someone was going to get her, and she needed the knives as protection."

Now, without Sam Asghari or anyone to truly make sure she's safe, the new video is extremely dangerous alarming to say the least.

Do you think Britney Spears is a danger to herself? Vote below.