if you do db.find().explain(), on a giant table, there is no way to ever kill it. you will see lines like the following in the currentOp output, with quickly incrementing getmore opid's

> db.currentOp()
{
"inprog" : [

{ "opid" : 205803, "active" : true, "lockType" : "read", "waitingForLock" : false, "secs_running" : 0, "op" : "getmore", "ns" : ......., "desc" : "conn" }

]
}