Silver_____nut for cats

I have seen pet shops selling some plant seed things that are brown, around 2cm long, that looks like a seed pod with little tiny bumps - presumably little seads.
i asked the assistant and was told that it works like cat nip. but i am a bit skeptical because what they tell you is very vague.

the name of the seed thing is called a "silver (something) nut" for felines?

Anyone heard of it before?
whats it for?

I've never heard of it. I did see a store selling a cat toy filled with honeysuckle which the package said works like catnip, but I have never heard of a silver nut?