I’ve been caught out many times when fiddling in the engine compartment or behind the dash and landed up with a deep scratch and blood everywhere!
When I was doing a recent job on the distributor on the MGB I spotted a definite lethal “spike” which was just waiting for a passing hand or finger to slice into!!
I remembered I had some spare trim plugs (the ones for the vent in front of the windscreen) which proved a perfect solution. Just had to squeeze the end with a pair off pliers.
Another option is to use a short length of vac advance tubing.