DO NOT RUN WITH A CLAY KNIFE: you could hurt either yourself or another person.
WEAR AN APRON: clay can stain clothing.
DO NOT EAT THE CLAY! it is not poisonous, but it is not good for you, either.
WASH HANDS AFTER HANDLING CLAY: as above... it is not poisonous, but not healthy to eat.
IF YOU DROP CLAY, PICK IT UP: the underfloor heating dries it out and the silicon can enter your lungs. Also, as it is wet, it is possible to slip on it.
KEEP IT IN A LARGE LUMP, NOT SPREAD OUT IN LITTLE PIECES: it can dry out too quickly if left in little pieces.
DO NOT THROW THE CLAY: it could go in someone's eye - the silicon could scratch an eye quite seriously. It is like small slivers of glass and is very sharp.
TIE HAIR BACK: it can obscure vision and get in the work being done.