Serena Williams explained that her sluggish performance in the Internazionali d'Italia third round against Christina McHale was because she became ill after trying dog food.
The world number one says she sampled "a spoonful" of the food that she gave to her dog, Chip, which left her feeling somewhat rough.
Williams subsequently lacked her usual bite against fellow American McHale, and trailed 4-2 before recovering to take the lead and powering to a 7-6 (9-7) 6-1 victory.
"I thought 'what the heck, I'm going to try a piece, it looks good'," Williams said.
"Fast forward two hours, I just ran to the toilet like I thought I was going to pass out. It did taste weird. It tasted kind of like house cleaner."
In a video posted on Snapchat, Williams added: "I force-swallowed it. I don't know what they put in these dog foods, but Chip liked it.
"I don't think it's consumable for humans. They should have wrote that! So now I feel really sick. It was just a spoonful, but I don't feel so good."
Williams has little time to pause for recovery, she faces Svetlana Kuznetsova for a place in the semi-finals on Friday.