Thermochromic toys have pigments that change their color depending on their temperature, meaning that you can observe such a toy beginning to change color simply from holding (or using) it. It's a neat effect, but it has special care requirements if you want to enjoy this color change for as long as possible. Do not use the boiling method to sanitize a toy with any thermochromic pigment in it. Use warm water and soap for regular care, and the bleach method for deeper cleaning if necessary. Do not leave exposed to UV light; keep them out of window sills, and maybe don't include them in lit displays, just in case. Do not leave/store toy in an area where it is at its 'hot' activation temperature (somewhere around 80 degrees Fahrenheit for most of these pigments). Somewhere between 70 and 75F is preferable. Any of the above conditions can prematurely cause the toy to 'lock' into one color and stop changing back. This doesn't void any warranties or affect the usage of the toy whatsoever, as the toy's primary function hasn't been compromised. Even with perfect care, it is possible that thermochromic pigments have a limited life span, so please keep that in mind when purchasing a toy that uses them.