SoftwareSerial

zakelectric:
You know what, I wasn't really sure what that was, but when I tried to remove it, the sketch quit working. There was some code after that that serial prints "BNO055 not connected" or something to that effect. I removed it since there's such limited memory on the ATTINY85.

I assumed it was necessary, what precisely is that there to do?

'bno.begin()' is absolutely necessary, to initialise the sensor. What I was querying was the fact that the code still continues on to use the sensor even if 'begin()' fails.

I think you changed the intent of the code when you removed the print line etc.

I'd be more likely to write something like:-

if (!bno.begin())
{
    mySerial.print(F("Failed to initialise the BNO055 sensor - cannot continue!"));
    while(true);    // Loop forever, (stop code execution).
}

so that you're informed of the problem if the sensor can't be initialised, then code execution stops.