A grammasite is a fictional parasite that feeds on words. It is native to the Thursday Next continuum, first appearing in Lost in a Good Book; agents who visit that world can become vulnerable to grammasites. Now that it is no longer a Quarantined Continuum, agents should be aware of the potential threat. Grammasites are parasitic creatures that can feed on both objects and characters. Different varieties feed on different parts of speech. In fictional characters, they can cause illness or even death. The treatment is to remove the grammasite from the afflicted individual as soon as possible.