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According to Schwarzenegger, the pranks that DeVito used to play on set even went as far as secretly putting cannabis into his cigar.
That meant that Arnie - who is a stickler for line-learning - had a complete mental blank when they went back to filming.
The pair used to enjoy their lunch together, before sitting down to enjoy a cigar. That's when DeVito decided to have a bit of fun.
Despite the fact that Arnie had spent ages learning all of his lines by heart, he couldn't remember a think after smoking his tampered-with cigar.
"He's a brutal prankster, and he's as funny in real life as he is on the screen," the former Californian governor explained in his monthly newsletter.
"I'm a fanatic about memorizing my lines so I never touch the script once I arrive on a set, but when we got back after lunch, Danny said his line and I just stood there. 'Duh.'"
In order to save a bit of time, director Ivan Reitman filmed some close-up shots of DeVito, who was creasing with laughter, which allowed Schwarzenegger to read his lines from a script.
Obviously, it's not very professional, and could have landed the pair in a pile of trouble if they'd been working with a less easy-going filmmaker.
Arnie admitted: "We were lucky this was on Ivan's movie because if this ever happened on a Jim Cameron film.
"We would have been in real trouble."
Schwarzenegger is no stranger to smoking a bit of pot, and has spoken freely about it in the past. In fact, he revealed to Men's Health earlier this year that he used to smoke weed with comedian - and notably stoner - Tommy Chong.
Yes, Tommy Chong of Cheech and Chong fame.
Arnie said: "Tommy and I became very good friends,
"We both had big, big dreams when we met on Venice Beach, working out there on the outside weightlifting platform, and we talked about how we wanted to be stars, and he wanted to be in comedy and was dreaming about that, and I was dreaming about being the biggest and best bodybuilder and getting into movies and being a leading man, and all of this stuff.
"So we had a really great time."
"And he was, of course, stoned a lot of times. And as a matter of fact, we went over to a friend's house many times to smoke pot in those days, and he actually taught me to not smoke a whole joint, but have a few hits and try to work out that way.
"So I started working out with a few hits, before we went to the gym and worked out this way, and it was really fantastic, I should say."
However, once he started to get properly focused on his bodybuilding and acting career, he packed it all in.
That is, until his special cigar with Danny DeVito, anyway.
Featured Image Credit: Universal Pictures
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