Hippo
This unique eye structure with T-shaped pupils is found in the four-eyed fish (Anableps). These fish have adapted to live near the water's surface, allowing them to simultaneously see above and below the waterline to detect predators and prey.
They are rectangular.
Animal pupils come all different shapes and sizes. A cat has slit shaped pupils, and a chicken has round pupils. Some goats even have time glass shaped pupils. Many different shapes.
Hippopotamus
Goats have retagular shaped pupils.
cuttlefish
Sheep
The shape of an octopus' pupil is square-shaped.
Goats. Also octopi. But octopi aren't mammals. Right?
Maltese painted frogs can have triangular shaped pupils. Please see the related link for more information...
There are several species of mongooses, with all studied specimens having horizontal-shaped pupils such as Herpestes auropunctatus, herpestes parvula, and Cynitctis penicillata. This is fairly unique as mongooses are some of the only predatory animals with horizontal pupils.
No, it is not more likely that a non T-shaped belly button will eject a piercing when compared to a T-shaped navel.