The whole biting a gold coin to see if it's solid gold, or gold plated lead was... yes to determine if you could deform it with your teeth - but no, if it deformed it was lead not gold. Whilst gold is very ductile (one of the most ductile metals in-fact which is how gold leaf gets so thin) it is harder - both in hardness, and in plastic+elastic deformation i.e. it's less mailable than a number of metals...
In other words, you can hammer it thinner, or draw it into smaller wire than lead - but you'll expend more energy reducing a piece of gold from state a to state b than you would taking lead through the same process (if possible)...