.There are 2 Thallium videos.
The 1.9mb video is of the below image. This video is provided to illustrate line intensity of the high purity metal standard, whereas the 3.2mb video illustrates a less intense thallium line originating from a pulverized rock sample. .

There is only 1 spectrum line for Thallium and if seen there is no doubt that it is present.

Spectrum line intensity can be an aid in determining the amount of an element present

8x – The solidified 999 pure Thallium bead is resting on graphite pad.
Notice the brownish-black oxide (sublimate) that was volatilized.
Good ventilation is required when analyzing this element.