From Mark Parker
Petersfield, Hampshire
You state that chimps eat certain leaves as roughage to brush out parasitic
worms (New Scientist, Science, 24 August, p 17). Domestic cats and dogs
daily swallow grass which they usually pass quickly in undigested tangles. They
seem to choose the longer blades, perhaps because the mechanical properties are
important or because the under-surfaces are hairier.
It seems likely that the behaviour has a similar de-worming purpose.
