The Kazleti are a warp-capable humanoid species. The Kazleti believe that experimentation on other species is an acceptable method of investigating their own physiology, and justify the inevitable harm caused by citing the number of Kazleti lives saved as a result. 80,000 Kazleti transported themselves to Earth territory. Their normal method of experimentation involves using an interphase cloaking device to render themselves, their ships and their devices both invisible and intangible. They then attach to the hull of a passing ship and spend several weeks carrying out experiments on the crew. These experiments range from changes in body chemistry to complex DNA manipulation carried out by cloaked tags, attached to a host's DNA.