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A 2000-2017 set of long-period comets with high-quality orbits of periheliondistance <1 AU is used to show that the objects that perish shortly beforeperihelion are nearly exclusively the Oort Cloud comets, especially those withperihelia within 0.6 AU of the Sun, intrinsically fainter, and dust poor. Theirpropensity for disintegration is much higher than predicted by Bortle'sperihelion survival rule, prompting the author to propose a new synoptic indexto be tested in future prognostication efforts. By their susceptibility todemise near the Sun, the nuclei of Oort Cloud comets differ dramatically fromthe nuclei of other long-period comets that almost always survive. In thisscenario, `Oumuamua -- discovered after perihelion -- is in all probability amajor piece of debris of an interstellar comet that was bound to perish nearperihelion if it was similar to, though much fainter than, the known Oort Cloudcomets. The nondetection of `Oumuamua by the Spitzer Space Telescope iscompatible with optical data for pancake shape, but not for cigar shape, withthe maximum dimension not exceeding 160 m (at an 0.1 albedo). Although thesolar radiation pressure induced nongravitational acceleration requires veryhigh porosity, `Oumuamua's estimated mass is orders of magnitude greater thanfor a cloud of unbound submicron-sized dust grains of equal cross section. Theacceleration could have displaced `Oumuamua by 250,000 km in 50 days,scattering other potential debris over a large volume of space.

1I/`Oumuamua and the Problem of Survival of Oort Cloud Comets Near the Sun