An influenza pandemic is an epidemic of an influenza virus that spreads on a worldwide scale and infects a large proportion of the world population. In contrast to the regular seasonal epidemics of influenza, these pandemics occur irregularly – there have been about nine influenza pandemics during the last 300 years. Pandemics can cause high levels of mortality, with the 1918 Spanish flu pandemic being the worst in recorded history; this pandemic was estimated to be responsible for the deaths of approximately 50–100 million people. There have been about three influenza pandemics in each century for the last 300 years, the most recent one being the 2009 flu pandemic.

Coronaviruses are a group of viruses that cause diseases in mammals and birds. In humans, coronaviruses cause respiratory tract infections that are typically mild, such as some cases of the common cold (among other possible causes, predominantly rhinoviruses), though rarer forms can be lethal, such as SARS, MERS, and COVID-19. Symptoms vary in other species: in chickens, they cause an upper respiratory tract disease, while in cows and pigs they cause diarrhea. There are yet to be vaccines or antiviral drugs to prevent or treat human coronavirus infections.

Botulinum toxin (Botox) is a neurotoxic protein produced by the bacterium Clostridium botulinum and related species. It prevents the release of the neurotransmitter acetylcholine from axon endings at the neuromuscular junction and thus causes flaccid paralysis. Infection with the bacterium causes the disease botulism. The toxin is also used commercially for medical and cosmetic purposes.

Walking (also known as ambulation) is one of the main gaits of locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined by an 'inverted pendulum' gait in which the body vaults over the stiff limb or limbs with each step. This applies regardless of the unusable number of limbs—even arthropods, with six, eight, or more limbs, walk.