Be careful what you lay on top of any metal heater! Well, Duh! Here's my toaster oven cautionary tale....
I got a call mid-morning one day at work saying my neighbor rescued my apartment, not to mention my two young felines, as the fire bells were going off and the thick smoke coming from my kitchen pointed to the culprit. My apt manager sounded mad asking me did I forget to shut off my toaster oven? I replied, No! I was too late to eat breakfast that morning, so I chugged some milk right from the jug and hurried on my way. The toaster oven was across the kitchen from the frig so I knew I hadn't messed up. The apt mgr seemed unsure! LOL
I left work early to see things for myself and to check on the kitties. The toaster oven was grandma's and I rarely used it being a fan of breakfast cereal and milk in those days. A wooden cutting board was always lying on top of the oven as it fit perfectly there. Of course I wouldn't leave it there while using the oven. The toaster oven got so hot that the wooden board was lucky to not have burst into flame. It became charred to the point of looking like it belonged in the fireplace. I was so grateful my neighbor was still at home to call for help!
The only thing I could guess what happened is that the kitties in all their crazyness ran across the top of the oven. Three buttons to contol the oven temp were on top - I remember yellow, orange and red buttons that you would press for low, med or high power. These kitties were at a really playful stage of their lives. I remember I had to put child locks on the kitchen cabinets in that apt as they would climb in there being delighted making all that noise among the pots and pans. The milk jug I hadn't even put back into the frig in my haste to get to work that morning. Later, I found it laying on its side in the hallway going to the living room. It had puncture marks from kitty claws in a couple places. I am sure they had fun, and their fill of milk. At least until the fire department came!
I have no idea if these toaster ovens are made with more sensible controls now. Perhaps the older ones still haunt your local thrift shop? Anyway, be forewarned! These things surely do get hot!