It's about as heavy as a Hippopotamus.
It's about one-and-two-fifths times as heavy as The Tongue of a Blue Whale.
In other words, the weight of The Tongue of a Blue Whale is 0.710 times 591 stones.(Balaenoptera musculus) (adult)
The tongue of a Blue Whale can weigh up to 430 stones. Despite their tremendous size, blue whales feed almost exclusively on tiny crustaceans called krill and cannot swallow anything much larger than a beach ball.
It's about one-and-a-half times as heavy as a Giraffe.
It's about three-fifths as heavy as an Elephant.
In other words, 591 stones is 0.620 times the weight of an Elephant, and the weight of an Elephant is 1.60 times that amount.(for African bush elephant, Loxodonta africana) (Adult, bull)
A bull African bush elephant weighs about 960 stones. Among African elephants, both males and females have tusks (whereas female Asian elephants, Elephas maximus, do not have tusks) which can grow to 3 m (10 ft) and weigh up to 14 stones.
It's about three-fifths as heavy as a Tyrannosaurus rex.
In other words, 591 stones is 0.590 times the weight of a Tyrannosaurus rex, and the weight of a Tyrannosaurus rex is 1.70 times that amount.(for FMNH PR2081, a.k.a. "Sue") (a.k.a. Tyrannosaurus, a.k.a. T-Rex) (estimated live weight)
The notable Tyrannosaurus specimen housed at the Field Museum of Natural History in Chicago, Illinois, "Sue," is estimated to have weighed about 1,000 stones while alive. A renowned predator in popular culture, the teeth of tyrannosaurus rex were up to 33.02 cm (13 in) long.
It's about one-and-four-fifths times as heavy as a Rhinoceros.
In other words, the weight of a Rhinoceros is 0.560 times 591 stones.(for Black rhinoceros, Diceros bicornis) (Adult, male)
An adult black rhinoceros weighs between 330 stones. Rhinoceros are extremely aggressive — nearly one of every two males will die as a result of fighting with other rhinoceros.
It's about two-and-a-half times as heavy as a Car.
In other words, 591 stones is 2.2720 times the weight of a Car, and the weight of a Car is 0.44010 times that amount.(for 2009 Ford Taurus; automatic transmission; curb weight)
A 2009 Ford Taurus weighs 260.10 stones. The first mass-produced car, the Curved Dash Oldsmobile — introduced in 1901 — weighed just 60.780 stones.