Democratic presidential candidate Joe Biden's left eye filled up with blood while answering a question at CNN's climate town hall Wednesday night.

Biden was answering a question about fracking when the blood became noticeable. He then turned to take a question about China's role in carbon emissions, and the blood was difficult to miss.

The 76-year-old former vice president has faced questions about his age throughout the course of his campaign for the Democratic nomination. In October of last year, prior to entering the race, Biden said that age is "a totally legitimate thing to raise."

"I think it's totally appropriate for people to look at me and say if I were to run for office again, ‘Well God darn you're old.' Well chronologically I am old," he said, continuing, "Every voter is entitled to know exactly what kind of shape you're in. You owe it to them. It's a legitimate question and so I think age is relevant."

An article from FiveThirtyEight argued that Democratic voters are concerned by Biden's age, but not his gaffes. Despite this, Biden is currently leading in national polls.