If someone in the household is allergic to molds that can grow in wood
pellets watch out for the ones which are sold very inexpensively.  A lot
of times they haven't been as protected from rain as the ones made for
litter.  We learned that the hard way when Steve got very ill and we
wound up chucking a great many pounds of pellets that had hidden mold.
(We also found out the hard way for him that the grain based litters can
have pollen in them.)
[Posted in FML issue 4686]