Nitrous Oxide expands greatly when exposed to heat.

$                   I was thinking that all O2 sensors would be
$somewhere in the throttle body

  No.  There's an airflow sensor of some sort in the intake system,
but the oxygen sensors are in the *exhaust* system.  The job of the
first one is to detect how much residual oxygen is in the exhaust
stream.  If there's too little, the mixture is too rich; if there's
too much, the mixture is too lean.  The correction in either case is for
the engine computer to adjust how much fuel is being injected.

  The first oxygen sensor is upstream of the catalytic converter.
The second oxygen sensor is downstream of the cat and is part of the
emissions control system, not the engine management system.

  I don't know how nitrous systems are used, but anything which puts
more oxygen into the intake stream without a corresponding increase in
fuel will result in too much oxygen being in the exhaust stream, and
when the first oxygen sensor tells the engine computer this, the computer
responds by delivering more fuel.  Whether the stock engine computer
on most cars has enough flexibility in its fuel delivery programs to
adjust fully for this, I have no idea; it may be that you would also
need to chip your engine computer as well.

`--------------------------------------' a vaguely phallic .signature