5 Min Read LONDON (Reuters) - From cat food to cannabis, it’s boom time for quirky ETFs offering the chance to punt on niche themes in fast-growth sectors, but their huge gains are unnerving some who see them as another price-inflated asset that may threaten market stability. FILE PHOTO: A statue of a girl facing the Wall St. Bull is seen in the financial district in New York, U.S., March 7, 2017. REUTERS/Brendan McDermid/File Photo While Reddit “gamestonks” have grabbed recent headlines, retail investors are also credited with large flows into exchange-traded funds - basically a tradable basket of shares - swelling their assets by more than $1 trillion last year, according to Refinitiv.