Can I play a reaction card in response to Bewitching Spiirit's triggered effect?

Yes, you can play a Reaction card in response to the triggered ability of Bewitching Spirit.

Here is the breakdown of why this is allowed:

1. Playing the Unit: When you play a unit card like Bewitching Spirit, it enters the board immediately and does not use the chain. You cannot react to the act of playing the unit itself (Rule 356.2/FAQ 9017).
2. The Triggered Ability: Once Bewitching Spirit is on the board, its "When you play me" ability triggers. This ability is a triggered ability that uses the chain (Rule 406.2).
3. The Response Window: Because the ability uses the chain, it becomes a "pending item" on the chain. Placing this item on the chain creates a window where players can play Reaction speed spells or abilities (Rule 406.4).

Important Note: You can only respond with a card that has the Reaction keyword. Because the chain is now "Closed" (it contains a pending triggered ability), you cannot play cards that are only Action speed.