RabbitHole is a custom RPC feature that protects Metamask users from front-running (aka 'sandwich attacks), directly within the 1inch user interface. It sends 1inch swap transactions directly to validators, allowing them to avoid the Ethereum mainnet mempool and the prying eyes of MEV bots hunting for victims. Currently the validators include Flashbots, BloXroute, Eden, and Manifold.
RabbitHole is designed as a layer between 1inch-Metamask users and Ethereum validators. It is very similar to the Flashbots feature but will only send users transactions to validators directly if there is a threat of sandwich attacks.