I've been off the boards for several days, so this won't apply the Morristhecat anymore, but anytime your cat appears to be straining in the litter box, a vet should be called right away. Although many things can cause straining, if it is a blockage it can be fatal within hours. Fortunately, Morris had no blockage so it was okay to wait to take him to the vet. But unless you know how to palpate a bladder and can rule out blockage (most lay persons can't) then always consider straining to be a veterinary emergency, especially if your cat is male and has a history of bladder infections.