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I could use the sense of smell by smelling the ruler fall causing me to close my hands. Taste would be even harder. Taste would work if you stick your tongue out and the ruler hit it making my hands close.
The nerves in my fingers help me catch the ruler as it falls when the pads of my fingers feel the touch of the ruler they know to pinch at the same time and not let go until I have secured the ruler with another part of my body.