Stephen Hawking might have one of the most respected voices in science, but it hasn’t always been his own. In 1985, Hawking—who is afflicted with amyotrophic lateral sclerosis, or ALS—caught pneumonia that led to a serious infection that required a tracheotomy. The intervention left him without the ability to speak. Ever since, the physicist has used a series of increasingly advanced text-to-speech synthesizers, all based around a now-distinctive voice that originated in the early 1980s with MIT engineer Dennis Klatt.

While Hawking has preferred Klatt’s version for decades, he’s not opposed to seeing what else is out there. In a comedic video created for the UK’s Red Nose Day biannual fundraiser, Hawking can be seen “auditioning” new voices, including Liam Neeson, Lin-Manuel Miranda, Anna Kendrick, Gordon Ramsay, Felicity Jones, and Eddie Redmayne, who won an Oscar for his portrayal of Hawking in 2014’s The Theory of Everything. You can see who impressed Hawking—and who didn’t—below.

[h/t Vulture]