Context: Death from laughter is a rare form of death, usually resulting from cardiac arrest or asphyxiation, caused by a fit of laughter. Instances of death by laughter have been recorded from the times of ancient Greece to the modern day.
 Question: can you have a heart attack from laughing Context: According to the theory of relativity, no information can travel faster than the speed of light in vacuum, but this does not mean that the refractive index cannot be lower than 1. The refractive index measures the phase velocity of light, which does not carry information. The phase velocity is the speed at which the crests of the wave move and can be faster than the speed of light in vacuum, and thereby give a refractive index below 1. This can occur close to resonance frequencies, for absorbing media, in plasmas, and for X-rays. In the X-ray regime the refractive indices are lower than but very close to 1 (exceptions close to some resonance frequencies). As an example, water has a refractive index of 6999999999740000000♠0.99999974 = 1 − 6993260000000000000♠2.6×10 for X-ray radiation at a photon energy of 6985480652946099999♠30 keV (0.04 nm wavelength).
 Question: can a refractive index be less than 1 Context: Wrought iron is an iron alloy with a very low carbon (less than 0.08%) content in contrast to cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which gives it a ``grain'' resembling wood that is visible when it is etched or bent to the point of failure. Wrought iron is tough, malleable, ductile, corrosion-resistant and easily welded. Before the development of effective methods of steelmaking and the availability of large quantities of steel, wrought iron was the most common form of malleable iron. It was given the name wrought because it was hammered, rolled or otherwise worked while hot enough to expel molten slag. The modern functional equivalent of wrought iron is mild or low carbon steel. Neither wrought iron nor mild steel contain enough carbon to be hardenable by heating and quenching.
 Question: is wrought iron the same as cast iron Context: Several unrelated groups of songbirds are called catbirds because of their wailing calls, which resemble a cat's meowing. The genus name Ailuroedus likewise is from the Greek for ``cat-singer'' or ``cat-voiced''.
 Question: is there such a thing as a catbird Context: Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust. Along convergent boundaries, subduction, or one plate moving under another, carries the lower one down into the mantle; the material lost is roughly balanced by the formation of new (oceanic) crust along divergent margins by seafloor spreading. In this way, the total surface of the lithosphere remains the same. This prediction of plate tectonics is also referred to as the conveyor belt principle. Earlier theories, since disproven, proposed gradual shrinking (contraction) or gradual expansion of the globe.
 Question: can a single tectonic plate contain both oceanic and continental crust
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