You can see where he is running because of his poison, if you're still gonna run into the poison then you deserve it.
Rumble can do the same thing with his flame spitter.
There's also surprise oneshot AP Nunu.
i'm sure there's others.
Singed does a shit ton of damage, if you let it build up that is. so if you're running after him (why are you?) and he runs into bush and you follow him you should still have seen where the poison was. if he's in the fog of war and you're getting hit, pls tell me his build i wanna be that fast. it's not like it's an invisible nid spear hitting half your health.