Skew. It can be a pain in the butt if you want to trade both delta neutral and probability neutral.
In QQQ, a delta neutral setup at the moment would be: selling a spread on the put side with the short put leg at the 275 (17 delta) and on the call side with the short call leg at the 344 (17 delta). However, this results in a short put strike 38 strikes away...
