"animals are not subject to procedures that involve pain or distress or would be required to use pain-relieving drugs. routin procedures such as injections and blood sampling from veins that produce only mild, transient pain or discomfort are reported in this category."

Category C animals are not subjected to procedures that involve pain or distress or would be required to use pain-relieving drugs. Routine procedures such as injections and blood sampling from veins that produce only mild, transient pain or discomfort are reported in this category.

i thinking chemical change