Done! Zombies will now deal damage when they get within 2.5 units of you. The damage starts at 5 HP per attack and increases by 2 each wave, with a cooldown of 1 second between attacks.

**Next Ideas:**
1. **Health Pickups** - Add medkits that spawn after killing zombies or between waves to restore health
2. **Melee Attack** - Add a close-range knife attack for when zombies get too close and you're out of ammo

**Ready to level up your game? Pick one and let's build it!**