I recently got a lava lamp. They take an hour or two to warm up before they become the trippy, moving “lava” they’re known for. Sometimes while warming, the blob inside becomes contorted into bizarre shapes. Usually they remind me of specimen jars in some mad scientist’s lab.
This time, it apparently transformed into a bird.
Edit to add:
Apparently we need a /c/MildlyPenis community.
There are best practices to follow, including keeping it away from heat sources and sunlight, making sure it's on a sturdy, heat-tolerable surface, and, yes, not leaving it on too long. (Though one hour is barely enough for the thing to heat up properly. What I'm finding online shows the limit to be around 8-12 hours. There might be different limits for different ones.) I keep mine on a tray table with nothing else on it, so it's isolated from anything flammable. Safety care instructions say that you can tell it's overheating if all the wax goes into one blob and stays near the top of the lamp.
Basically, as long as you follow the safety advice that comes with it and don't leave it on too long, it should be safe.