😆 Right on humans and dolphins. Actually just about all whales can sing (little sub-trivia: the songs of the blue whale also hold the record for loudest sound made by a animal; 180 decibels!!!)
Other known singing mammals are bats, and as recently discovered, mice! That's right, the males sing for the females as a mating request. Only it's done in ultrasound, so we can't hear it.
Romantic little furballs
Bill Gates’s 2.6 billion notes divided by 156 equals 16.7 million layers of £10 notes. A £10 note is approximately 0.1mm thick, so with 16.7 million layers, this makes the stack of notes some 1.67 kilometres (just over one mile) high. Terminal velocity, the speed at which an object falls to the ground, from this height would be around 125 miles per hour, similar to a person free-falling from a plane. So should Mr Gates fall out of bed, he would take just under 30 seconds to hit the floor.
You could become rich by releasing your own single!