It works based on the diamagnetism of water. Water has a very small response to magnetic fields. As a result, if you apply a large enough field, you can exert a

It works based on the diamagnetism of water. Water has a very small response to magnetic fields. As a result, if you apply a large enough field, you can exert a significant force. The scaling problems are that this requires massive magnetic field (even for mice). Generating such things is nontrivial.