With SAPI's voice recognition, you need to define the words you want the speech engine to recognize. Maybe if you add the word "ACHOO!" (or however your sneeze sound

) in your dictionary then it would recognize your sneeze.
I'll have to try this with my voice reco app.
Code:
<RULE NAME="speak" ID="RID_Speak" TOPLEVEL="ACTIVE">
<L PROPNAME="speakvalue">
<P VALSTR="Bless you.">Achoo</P>
</L>
</RULE>