“Books on ‘Hindu feats’ became available throughout the twentieth century, explaining such classic Indian wonders as snake charming and ‘the bed of nails’, but also including a wide range of potentially dangerous demonstrations that were less obviously Indian. These were the books to read if you were interested in ‘Driving a spike into your head’, ‘Eating a ball of fire’, or the equally imaginatively entitled ‘Car on head’. More delicate readers could relax at home with one of the more gentle ‘feats of the yogi’, such as ‘hypnotizing a rabbit’. But anyone attempting the more adventurous pastimes would do well to read the instructions carefully. ‘Chewing molten lead’, for example, required a special compound that ‘melts at approximately 160 degrees. If you wish a lower melting point, add to the above a small amount of quicksilver… When melted, this mixture may be poured on the tongue which, it goes without saying, must be moist with saliva.’ And if the student was not convinced by that explanation, the following assurance of the author was given: ‘Personally, I have never developed enough courage to try this, although several have told me it is OK.'”
Peter Lamont, The Rise Of The Indian Rope Trick (2004), quoting from Thrilling Magic by Leonard H Miller (1959)
Gallium is not particularly poisonous and melts at skin temperature, it would be fun to play with if it didn’t stain ones palms black… but now that I think of it, yelling “Gahh!” and revealing a blackened tongue would by a good way to end to the act.