As already pointed out, only below ~64 km/h (~40 mph) can one shift into Neutral without the ICE needing to spin in order to protect MG1 from over-revving. Normally it would be spun by MG1 with electrical power supplied by MG2. Droid13 and Pete4 make the interesting point that, since in 'N' all power flow to/from the MG's (and consequently also your regenerative braking) is supposedly cut, the ICE cannot be spun in this way by MG1, and must thus be fired up under gasoline power to protect MG1. But how can this be done without using MG1 to restart the ICE? Well, if the car was in fuel-cut mode when it was put into 'N', then the ICE was already spinning at ~1000 rpm, and so could presumably be fired up instantaneously without any problem. This is just how the TCH normally switches into and out of "fuel-cut" mode while driving in 'D' (see below). But if the car was accelerating in 'READY' and 'N' under gravity from rest down a hill, starting with the ICE off, how would it start the ICE to protect MG1? I don't know. I'd guess that, since the NiMH battery and all electronics are still active because the car is still in READY, it would go ahead and use MG1 to start up the ICE for protective purposes when the speed reached ~64 km/h. Would someone like to check this out?

Talking about "heretical" mode, without instrumentation more sophisticated than the car's MFD or a ScanGauge, I don't think it's easy to determine exactly when the TCH is in this mode. In addition to the ICE's speed, one needs to be able to monitor MG1's speed, and also its direction of rotation. I believe that heretical mode is commonly employed when travelling at steady high speeds on relatively flat highways. It should not be confused with fuel-cut mode which can occur at speeds above ~64 km/h when the car is coasting (or, at least, when the accelerator is only very lightly pressed). In fuel-cut mode, all fuel flow to the ICE is stopped, but it is being spun at ~1000 rpm by MG1 (powered by electricity from MG2), in order to prevent it from the over-revving that would occur were the ICE allowed to stop completely. Fuel-cut mode can be detected unambiguously from the fact that ScanGauge shows "open-loop" ICE operation, and the dash's FE gauge simultaneously reads precisely zero fuel usage (0 L/100 km or 60 mpgUS). In both cases, electrical power is flowing from MG2 to MG1. The open-loop indication would, however, clearly distinguish fuel-cut mode from heretical mode.

Stan