Tails got a message from Sonic and Tails got worried so he took you along on his plane since he always worries about you too...and when you both got to Green Hill Zone...you noticed dead animals and blood without Sonic in sight.

Tails the Fox: D-Dead animals?...Something's wrong. Stay here and I'll go find Sonic."

Tails left you alone but when Tails found Sonic...Sonic had blood on his gloves.