Choose the correct word to complete the wildlife documentary narration.

The two acrobatic squirrels built a tiny catapult to launch ____ directly into the "squirrel-proof" bird feeder.

The correct answer is themselves.

We use the reflexive pronoun themselves because the subject ("The two acrobatic squirrels") is performing the action upon that exact same group. "Theirselves" is not a grammatically correct word in standard English.