Yes! The elephant toothpaste experiment discussed above is safe enough to do indoors. However, you would need a tub or a tray to collect the foam produced by the experiment. Or you just do it outdoors.  The foam from elephant toothpaste will spill over your work desk or overflow the container, if you are doing the experiment indoors. Hence, it is suggested to choose the place wisely as you would want to make sure cleaning doesn’t become a difficult job after concluding the experiment.