Just what humankind needed: the 21st century version of mood rings.

Japanese inventor Shota Ishiwatari believes he has made that possible with "Tailly," a robotic tail that reacts with the wearer’s heart rate, wagging rapidly when the owner is excited and it simply hangs down when the human has a normal heartbeat, Geobeats reported.

Ishiwatari, who is currently trying to get $100,000 in funding for the technological tail after a failed drive on Kickstarter, insists the Tailly is not a mere toy, a fashion accessory or a gadget. It's actually all three combined into one amazing device.

He predicts the device will be especially helpful to couples who will be able to express their true feelings when mere words aren't enough, according to Geekosystem.com.

As kooky as Tailly may seem, it's not the only robotic tail currently in development.

The company behind Tailly is also working on "Shippo," a robotic tail that uses brainwaves instead of heartbeats.