- GnadeMasta
- |
- Honorable Legendary Member
It likely has a little sensor inside that looks for some sort of biological or heat signature, or maybe both, or something else.
It likely then releases some sort of chemical on the grenade, causing that weird flames effect on the outside to become adhesive, and activates a countdown timer.
When the timer goes off, it likely releases a little plasma core to make an explosion, vaporizing the grenade and anything close enough to the explosion.
/speculation