Why does brown rat have strong teeth and it is comparable to steel

Rat teeth are ranked 5.5 on this scale, which means their teeth are harder than copper and iron. The jaw muscles of a rat can exert up to 12 tons (or 24,000 pounds) per square inch. By comparison, a great white shark bites with a force of 1.8 to 2 tons per square inch

. The scale ranks from 1 (softest, such as Talc) to 10 (hardest, such as Diamonds).  Rat teeth rank about 5.5 on the Mohs Scale, harder than iron or copper.  Human tooth enamel only ranks about 5 on the Mohs Scale.  Because their teeth are so hard, rats are able to chew through most of the materials people use to keep them out, such as:

comfortable

explanation:

one type of the adjectives is predicate adjective. a predicate adjective is an adjective which follows a linking verb and modifies or refers back to the main subject of that linking verb.

it usually is used just before the noun it modies.

here in this example:

'penguins seem comfortable in the coolest habitats', comfortable is the predicate adjective which follows the linking verb 'seem' and modifies the noun.

what book are we talking about here