When the female flea feeds on your pet's blood the chemical in Program enters her eggs and causes a change in the egg that prevents them from hatching.
(the female flea; feeds; on your pet's blood) (the chemical in Program; enters; her eggs; T:When the female flea feeds on your pet's blood) (the chemical in Program; causes; a change in the egg; T:When the female flea feeds on your pet's blood) (the egg; prevents; them; from hatching) (them; from hatching; )
the female flea the chemical in Program the chemical in Program the egg them
feeds enters causes prevents from hatching
on your pet's blood
her eggs T:When the female flea feeds on your pet's blood
a change in the egg T:When the female flea feeds on your pet's blood
them from hatching