This prank is embarrassingly easy but lots of fun for April Fool's Day or a quick prank.
Obviously you can choose which ever animal (or message) your prefer to appear on the bottom of your friend's drinking vessel.
In this example, we chose a pig's snout.
Step 1: Sourcing and Sticking
Trawl through your books or the web to find a good quality photograph of snout.
Once you are happy that your image is the right size, print it out on photo paper.
Laminate and cut to size
Using double-sided adhesive tape, stick it on the bottom of a mug, beer bottle or drinking vessel of your victim
(assuming your victim is right-handed, the handle should be on the left hand side of the vessel when upturned).