To fly, the boys need a check up from the vet, and he issues health certificates for them. Part of this procedure is to check their stool samples.
Unfortunately, Whitey's sample came back positive for parasites. This means two weeks of daily doses of drugs for both boys, since they share litter boxes. Once the regimen is completed, they will need to be checked again by a vet in Washington.
It doesn't prevent issuing the health certificates, thank goodness, since that would prevent them flying on the appointed day.