"I have eight arms, three hearts, and blue blood. I can change colour in an instant. I am considered the most intelligent invertebrate on Earth. What am I?"

Answer: An Octopus. Octopuses have three hearts and blue blood (due to copper-based haemocyanin instead of iron-based haemoglobin). They can change colour and texture in milliseconds. They are remarkably intelligent, capable of solving puzzles and opening jars.