(WJAR/NBC News) A Massachusetts man is in critical condition after attempting to melt down mercury dental fillings, believing they contained silver.

On January 25 the man took a bag of unused dental fillings that he had received from his grandfather, who was a dentist, and attempted to melt them on the stove to get silver to sell for cash.

"He was bored at home," his girlfriend, who did not want to be identified, said. "We were having trouble with transportation. We did lose our truck, and we needed another vehicle."

The very next day, she said their dog died and then her boyfriend started acting strange.

"He was just using a water bottle thinking it was his cellphone trying to play a game on it," she said.

On Monday, she said he went to the hospital and was originally treated for pneumonia.

Within the week her three cats started acting odd and have since died.

While he was in the hospital, she went looking for an explanation.

"I spoke with his sister. She said there's no such thing as liquid silver. It had to be mercury," she said.

Read more on WJAR's website