I'm trying to examine the communication of a USB mouse with an oscilloscope (PicoScope 3204). When I connect the scope's ground to one of the two data signal lines (Data+ or Data-) the mouse shuts down. The mouse is the 1995 Microsoft Home device, so it must be using USB 1.1, not some fancy high-speed version. I also tried the same on a USB memory stick and experienced the same problem. Is there an simple circuit I can build to overcome this problem?
I'm aware there are sophisticated USB test fixtures for this purpose, but I'm trying this as a demonstration/experiment, so I'm looking for a minimal home-brew solution.