|I heard the mother fern was bad incase your cat maybe took a bite out of it??|
|A quick search of several databases of poisonous plants beginning with the Cornell University listing and related links|
did not bring up any references to Asplenium bulbiferum or mother fern. However, this could simply mean there are just no cases reported.
In general, it is not a good idea to allow a cat to nibble on your houseplants (for both the plants and the cat), so perhaps you can cage the plants or keep them in a separate room if you have a cat who likes to eat them routinely. Some people have had success using a commerical repellent sprayed on the plants to train the cat to leave the plants alone.
If you have a concern about a cat eating something it shouild not have, it is usually a good idea to call the veterinarian right away and get an immediate answer in case emergency measures should be taken.