to gauge whether an opening is wide enough for their body to pass through. This is sometimes supported by the statement that the whiskers of individual cats extend out to about the same width as the cat's body, but at least two informal reports indicate that whisker length is genetically determined and does not vary as the cat grows thinner or fatter. In the laboratory, rats are able to accurately (within 5–10%) discriminate the size of an opening, so it seems likely that cats can use their whiskers for this purpose. However, reports of cats, particularly kittens, with their heads firmly stuck in some discarded receptacle are commonplace indicating that if a cat has this information available, it does not always make best use of it. Marine mammals Pinnipeds have well-developed tactile senses. Their mystacial vibrissae have ten times the innervation of terrestrial mammals, allowing them to effectively detect vibrations in the water. These vibrations are generated, for example, when a fish swims through water. Detecting vibrations is useful when the animals are foraging and may add to or even replace vision, particularly in darkness. Harbor seals have been observed following varying paths of other organisms that swam ahead several minutes before, similar to a dog following a scent trail, and even to discriminate the species and the size of the fish responsible for the trail. Blind ringed seals have even been observed successfully hunting on their own in Lake Saimaa, likely relying on their vibrissae to gain sensory information and catch prey. Unlike terrestrial mammals, such as rodents, pinnipeds do not move their vibrissae over an object when examining it but instead extend their moveable whiskers and keep them in the same position. By holding their vibrissae steady, pinnipeds are able to maximize their detection ability. The vibrissae of seals are undulated and wavy while sea lion and walrus vibrissae are smooth. Research is ongoing to determine the function, if any, of these shapes on detection ability. The vibrissa's angle relative to the flow, and not the fiber shape, however, seems to be the most important factor. Most cetaceans have whiskers at birth but they are typically lost during maturation. The follicles and any vestigial hair sometimes function as touch or electrical sense organs. Lines of research Neuroscience A large part of the brain of whisker-specialist mammals is involved in the processing of nerve impulses from vibrissae, a fact