On Thursday, Radcliffe, 25, stopped by Conan to talk about his new movie Horns and discuss a particularly scary moment from the set.
The film was shot in Canada, which meant things could get quite chilly. To prevent the pipes in Radcliffe’s trailer from freezing, the crew added antifreeze to the water, but no one remembered to tell the star about the toxic addition.
“It’s all non-potable water that comes out the tap,” Radcliffe told host Conan O’Brien. “I did not know that! So I drank a full cup of non-potable water. So, I guess, like half antifreeze, or whatever it would’ve been.”
While Radcliffe now seems unscathed by the incident, he said the accidental self-poisoning left him feeling seriously ill for three days.
Horns, Radcliffe’s apparently life-threatening new film, is currently out in theaters.