Goofs

When Sherlock Holmes is fishing in Scotland, first the river current is flowing from left to right. Later as he walks off screen right, downstream, he's walking upstream and the current is flowing right to left. In the next shot the current is back to flowing left to right.

Homes 'corrects' the fake Matthew Ordway by saying that Ordway should have said that 'the virus [of the spiders] was valuable to toxicologists.' He should have said venom, not virus.

When the impostor posing as Matthew Ordway knocks a terrarium of black widow spiders onto the floor and Watson reaches for the gun among them, Holmes shouts "Stop it, Watson! Those insects are deadly!" Spiders are not insects, and Holmes, having just revealed Ordway to be an impostor on the basis of the man's lack of knowledge about spiders, should know this.

Adam Gilflower is summoned by Holmes to identify the dead spider because, says Holmes, "I believe you know more about spiders than any man in London." Gilflower identifies the spider, but incorrectly observes that it is "the deadliest insect known to science."

Insurance companies won't pay off on suicide, yet the Spider Woman deliberately makes these murders look like suicide to collect on the life insurance. In reality she wouldn't collect a dime.

The first time Sherlock Holmes refers to the deadly spider that caused all of the suicides and nearly killed him, he calls it an "insect". Spider are "arachnids", which have 8-legs and 2 body segments, unlike "insects" which are 6-legged and have 3 body segments. Holmes is unlikely to make such a mistake.

When Adrea Spedding tells Norman to send a car for Rajni Singh (Sherlock Holmes in disguise), he mouths "alright" but there is no audio.

At the beginning of the film, Holmes appears to be fly-fishing in white water rapids.

When Watson discovers the skeleton on the closet, it's three-dimensional, but after he brings it out into the light it's a two-dimensional flat.

When Dr. Watson plays the tuba (c.29 minutes) he is clearly miming and his fingering of the valves bears no relationship to the notes that are heard.