"Just" A Mouse

Euthanizing animals brings up a plethora of emotions including compassion, guilt and doubt. What your relationship is with the animal also tends to dictate what emotional path you may go down. Pet owner, veterinary professional and animal welfare personnel may all feel a different level or attachment or detachment. But what about lab animal professionals? These folks work with research animals to find cures, therapies, discoveries and innovations that extend lives to humans and animals. So how do the folks that dedicate their lives to lab animal research cope with the levels of euthanasia they perform? Especially if it's "just" a mouse.