The strangest thing about the octopus.

There are many, many strange things about the octopus.

• They have three hearts.
• They're the only invertebrates capable of using tools.
• They can open childproof pill bottles.   

But here is the strangest:

There are three plural forms of octopus:

octopuses, octopi, and octopodes

• Currently, octopuses is the most common plural form in the US as well as the UK. 
• Octopodes is rarely used but perfectly acceptable.
• Octopi is frequently used but considered incorrect by most grammarians.