There are many situations when doing card magic where it is useful to know the bottom card of the pack. As a magician does not wish to make this obvious to his audience, it is important to find a way of doing this secretly and without arousing suspicion.
There are various ways of sneaking a peek at cards and here are various methods:
One method is to hold the pack face down in the right-hand, the thumb on the near short side and the fingers on the far short side (see photo right) and to make a gesture of squaring up the deck by tapping the right-hand long side of the pack on the table giving the opportunity of sighting the bottom card.
Another method is to hold the pack in the right-hand as above and be in the process of explaining what you're about to do with your next trick. As you are talking, it is possible to open your arms slightly and turned your palms half upwards so that you're able to casually peek at the bottom card before you turn the palms face down again and possibly perform one of the false shuffles to keep the bottom card in the same place.
Finally, if you have any reason whatsoever to hand the pack of cards to a volunteer or spectator then this is always a good opportunity to glimpse the bottom card of the pack before having the cards returned to you and performing a false shuffle. Indeed if there is a heckler or awkward character in your audience, it is quite natural gesture to offer the pack to them and to ask if they feel that they could do better! This makes it exceedingly easy to glimpse the bottom card.