Catcrass is grass - mostly barley or oat grass, preferably grown indoors so
that when the cat eats it, they won't ingest parasite eggs (like cows and
other grazing animals do).  It aids in the passing of hairballs, they get
veggie-vitamins from it and sometimes it makes them throw up (another aid to
the reverse-elimination of hairballs).

Catnip is an herb, a member of the mint family, is a leafy green plant that
some cats go loco when they come in contact with - while others ignore.