(set theory) The paradox that a set defined to contain all sets which do not contain themselves can neither consistently contain itself nor not contain itself.

Alternative letter-case form of Fermi paradox

(biology, exobiology) The seeming contradiction, serving as a challenge to believers in the existence of advanced lifeforms throughout the universe, that there is no scientific evidence that extraterrestrial civilizations have tried to visit or communicate with Earth.

The observation that the association of two variables for one subset of a population may be similar to the association of those variables in another subset, but different from the association of the variables in the total population.

The observation that the French suffer a relatively low incidence of coronary heart disease, despite having a diet relatively rich in saturated fats.

Pseudis paradoxa, a species of frog unusual because it is larger as a tadpole (up to 25 cm or 10 in. long) than as an adult (about a quarter of that length).

A time travel paradox in which the consequences of an event in the future travel back in time and cause an event in the past or present, which in turn is among the causes of the first event, forming a causal loop in which each event is caused by the other.

The paradox of time travel in which inconsistencies emerge through changing the past.

(rare) The statistical and psychological observation that a person is prone to prefer Coca-Cola over Pepsi when they have labels, but prone to prefer Pepsi over Coca-Cola when they are unlabelled.

Removal of one's clothes while in a state of hypothermia.