Which animal has the largest brain relative to body size?

If you mean all animals, very small insects such as bumblebees have brains that are large relative to their body size. If you mean mammals, some shrews are often cited among the highest in brain-to-body ratio. This is a tricky question because different groups are not directly comparable, and scientists often use different measures such as encephalization quotient. The best-known general answer is that tiny animals often have disproportionately large brains for their size.