A waiter at the party near the beginning has a tray full of drinks. He goes behind a few people, not seeming to stop, and yet he arrives at Van Heflin with only his single drink on the tray.
The voiceover at the beginning refers to the black widow as the deadliest of all spiders. Actually, the Sydney funnel-web spider, native to Australia, is considered the deadliest. Its bite can be fatal within 15 minutes if left untreated. There is an anti-venom for it, however.
If one listens carefully for changes in presence, it appears that some of Van Heflin's dialogue was looped in post-production.